Probably a bit of a few things

1) CM is gone and other ones that were small under used are now being used & promoted more. It was tough to fight CM
2) CM is gone and people who were thinking about setting one up decided to see if they could make a go at it
3) Privacy is being discussed more and more so more people are looking for mixers
4) Some are probably 'white label' mixers [ https://en.wikipedia.org/wiki/White-label_product ] so spinning one up was not much work.
5) Other?

Could be other reasons too but I would think those 4 are the big ones.

-Dave

Bitcoin mixer industry currently has a thriving market, and CM has vanished. The public demands alternative mixer services to safeguard their privacy. Numerous Bitcoin mixing websites have started promoting their services to meet the market's needs.

To ensure a safer experience with mixers, you can refer to a curated list of trusted Bitcoin Mixers compiled by @LeGaulois. In that thread, you will find additional information such as official mixer website links to avoid scams, Tor links, official threads on Bitcointalk, service fees, and minimum amounts required for using mixing services.

2023 List Bitcoin Mixers Bitcoin Tumblers Websites

Meanwhile, any suspected scam Bitcoin mixing services will be continually updated in this thread.

Scams Bitcoin Mixers List and Services closed

You can learn to identify the characteristics of scam mixer services by referring to the compiled list. It is highly recommended to utilize well-established mixer services that have been in operation for several years, rather than opting for newly launched mixer services. Always pay attention to both clearnet and Tor links to ensure that you don't end up visiting the wrong websites.

Funny that I saw a couple of people already mentioning that it's because Chipmixer was gone, when even during Nov 2022 a lot of mixers have been popping up out of nowhere. I guess it's just because there's money to be made in this type of cryptocurrency business, and since there's not much work really, especially if you're White label mixers like what DaveF mentioned since there's not much work to do it, which means more cashflow for these people. It's still probable that it's because of Chipmixer that these mixers suddenly gained confidence, but that only counts for those that have been here after Feb, for the rest of the bunch, I don't think that's the reasons for their existence.

Because privacy become more uncommon these days, from different crypto regulations and the rise of chain analysis. Also, there's a huge market  in crypto mixers, not just for bitcoin but for some alts too.

Maybe you weren't so observant back then, but there were a fair number of mixers around before Chipmixer came into the picture and even after they established themselves. The difference is they weren't advertising so much in the forum like Chipmixer did. Bestmixer's and bitblender's stay was short-lived, but they were two of the few mixers that tried to compete with Chipmixer while advertising here in the forum. After their demise, Chipmixer remained dominant until recently.

Yomix among other mixers were operational some months before Chipmixer was shutdown.

I think Dave said it all, chipmixer was a force that couldn't be contended with, for as long as it was running, it was like it buried every other mixers to the background, if we try to find out when this other mixers were launched, we might discover that most of them were not launched this year, some were probably launched last year, and other launched the year before last year, but the presence of chipmixer seemed to have thwarted all their efforts to try to come to the limelight,  and now that chipmixer is no more, we see all of the other mixers springing up, like they were launched yesterday, it's like a jailer that died, and the prisoners set free.

Supply and demand. ChipMixer was a solution that was seemingly unbeatable. It had (seemingly) good administration, it was (seemingly) untouchable and it (seemingly) did the job for those looking for privacy. As soon as it was seized, many old mixers began their advertising campaigns and news ones stepped in to try and take some of the large market-share wedge that ChipMixer left behind, with the additional opportunity of being a 'better' solution.

I don't believe there is white-label software for mixers as DaveF said. However if this is true, that would definitely lower the entry barrier and allow virtually anyone to get into the market cheaply and easily.

I'm not convinced that they decided to advertise because Chipmixer is no longer operational though. If I'm not wrong, some mixers already promoted themselves even before Chipmixer closed down. Sure, some of them increase their budget, but they already have a relatively high budget to begin with. If anything, I guess they find that signature advertising is one of the most effective ways to build their brand awareness compared to other alternatives.

Is there any case where a hacker knows what address you own and then simply 'hacks' your wallet? That being said, what you said definitely relates to privacy issues. If anything, they can send spam e-mails or something similar if they find your personal information.

Chipmixer is seized by the government and pretty much mixing is a profitable business. Just by looking at the campaign alone, you can see a bunch of it, and all of it pay a heavy amount of money for signature. The business is high profitable just like gambling that is why is all over the place and after the chipmixer is gone there is a big hole and everyone want fill that hole.

Perhaps the correct question is why so many mixers are  started signature campaigns here, and the reason for this is the increase in the number of users who are beginning to care about privacy, especially since solutions such as coinjoin are questionable in their ability to hide identity.

Wasabi Wallet’s CoinJoin Coordinator to Blacklist Certain Bitcoin Transactions

This news was in the year 2022, and here, many users are using mixing services, and with the absence of a ChipMixer, this market has become in need of many alternatives, which are now limited to less than 6 mixing services, while in the past there were many.