Exactly. If I was in their place, I'd demand Dogecoin, just to be
funny and to bring the price up a bit. Imagine the news articles.

They don't necessarily use Bitcoin due to its anonymity (it's not completely anonymous) but more like because it is the most widely known decentralized cryptocurrency.
They could easily use Monero and be 1000% untraceable, but it is much harder to acquire (as you'd have to buy Bitcoin anyway).

Hackers would like to paid by bitcoin because of it is untrackable anonimity feature. So when you do a dirty job, you don't wannt be caught while you're getting paid.

This just isn't true. Bitcoin is pseudo-anonymous, and very easily traceable. Especially if you know the attacker's address, tracing it is easy. However, the chain can be broken by mixers or other online wallets.

The main reason it is used is because it is completely irreversible. Once they have the money, nobody can forcibly take it away from them.

Bitcoin appeals to hackers simply because it is digital money, and hackers work digitally. Bitcoin really isn't as anonymous as many people claim -- the ledger is public and can be tracked by anyone. A slick hacker can work anonymously, just like criminals can work anonymously with cash. I'm guessing once the bitcoin is obtained the hackers then convert their bitcoin to an actual anonymous coin, such as Monero.

Because Bitcoin is very secure that why many countries do not legalized Bitcoin cause they can totally control it. It's very difficult to find out who is the owner of any transaction. Crimes often take advantage of this case to commit crime such as drug trafficking or money laundering and the biggest money laundering related to Bitcoin I've ever known is Btc-e )

Hackers that asked for ransom in bitcoin have it at the back of their mind that they the chances of them being caught is very little and with the sophisticated technological break through, its possible they are never caught.

On the issue of whether they can be tracked or not? Yes they can if the relevant government dedicate its resources home and abroad to finding them but the question to ask is that, they money they are after, will it even be enough to cover the costs of going after them?.

Although, going after the hackers will the toughs but that does not mean they cannot be caught. It might take time compared to if they use fiat, but its not forever. It has happened before and it will still happen so they should not rejoice yet.

Maybe also because they can take it anywhere they want without the risk of being flagged by airport officers or risking having too much money on the bag. They can easily store, spend and launder it. No one tags someone who spends ten thousands of bitcoin but do that in dollars and you will be tagged by IRS.

breaking into the system for his own interests and asking for a ransom, this is a crime and certainly they don't want to be detected
therefore they request paid through bitcoin or other cryptocurrency,so it is not easily detected its existence