The investors already know the motivation of HODLers from a long time ago. They can hodl their Bitcoin and not panic or worry if anything happen to Bitcoin and even they can use that for their own benefit. When others don't believe that Bitcoin price can increase like today, they still believe and buying Bitcoin for more.

They know what they believe now will gives something big to them and that is prove right now. They now can sell their Bitcoin at $100k or more and takes their profit and enjoy it. While they can prepare some money to reinvest in Bitcoin when the price is down.

The other currencies? Do you mean altcoins? That impact altcoin too as many of them increase and could make a new ATH later. The other coins can follow Bitcoin and that is the effect that could happen in the market. We can wait for that and make sure we are involve in the big party.

Bitcoin is the foundation of the crypto industry. All other cryptocurrencies are, to varying degrees, copies of Bitcoin.

Some of them are direct forks (e.g., LiteCoin, Dogecoin, Bitcoin Cash), others are coins with an emphasis on privacy and anonymity (e.g., Monero, ZCash), and others are coins with a developed smart contract system (in particular, Ethereum, Neo, Tron, Solana, etc.).

With all the variety of coins, tokens, NFTs, etc., the primary source of their origin is Bitcoin. Institutions also single out the first cryptocurrency from all other coins.

Alternative cryptocurrencies can be considered a kind of experimental laboratories in which technological, financial and social solutions are tested, which will subsequently be implemented in the Bitcoin code.

Bitcoin is simply the tide that raises all boats.  Nothing more (almost entirely) nothing left.  99.9% of altcoins are truly what their nickname is, pure shit (shitcoins).

Yeah sure if you're lookin to make some money trading, then bitcoin does a great job of help create upside potential for altcoins.  Bitcoin does well, the tide rises. 

The problem is then you're holding on to shit bags which means how are you goin to know when to dump them?  A game I'm done playing.

Bitcoin is the lifeblood of the crypto market. It's the foundation, the crypto that brings out the best in crypto market. Altcoins are just alternative coins that were created from the image of bitcoin. Whatever the success of bitcoin, the effect will also be carried out by the altcoins. It's just that altcoins are less dominant, but they still have the potentials to succeed in the future, next to bitcoin.

yeah this is the reality now, the BTC.D just hardly go down, and it seems it can even go higher, because institutional investors money are centralized on bitcoin and altcoins don't even get the share of pie  .
maybe it's also people actually figuring out that BTC is the hot thing right now so they cancelled their strategy of rotating to altcoin, proven from them BTC.D chart where there's impulsive rotation from alt to BTC within a matter of hours or even less.

so the effect of bitcoin growth in this case for other currency isn't that significant, it seems BTC just want to go high without any alts following.

Bitcoin is a biggest cryptocurrency in market cap and big institutional investors with massive capital from traditional markets, if want to join cryptocurrency market, surely will pay their attention and spend their capital firstly into Bitcoin. They have massive capital in management and capital safety is their first and vital priority, profit is a less important concern with them, maybe only at the second position in priority list.

Bitcoin besides biggest market cap, highest trading volume that are helpful for institutional investors with entries and exits, has other big advantages.

In security of blockchain, it's a safest one with biggest network hash rate. Together with Proof of Work algorithm, Bitcoin blockchain gives highest safety for fund transfers.
https://howmanyconfs.com/

Altcoins are different, even with PoW algorithm, they have worse security, and if its blockchain is based on Proof of Stake, Smart Contract, other algorithms, it's worse.

Many altcoins have died since 2009.
How many (altcoin) cryptocurrencies have failed?

Bitcoin rise above $100,000 attracted new people into crypto, and it also lead people into altcoin market, but all altcoins benefit equally. Many of altcoins is not well established many others also has sketchy background. While Bitcoin's success opens doors to the industry, it does not guarantee a breakthrough for others. Altcoins with strong use cases and community support may thrive, but most of them battle to rival Bitcoin in acceptance and appeal, making their success dependent on how well they navigate adoption and regulatory challenges.

Yes, the impact of Bitcoin on Altcoin is very large, both in actual terms and emotionally, as any rise in the price of Bitcoin leads to a rise in Altcoin and vice versa.

This is in the short term, but in the long term, many people buy Altcoin because they believe that it will grow like Bitcoin did, as it started at a price of about a few cents to reach above $100K, but in reality they are wrong. Altcoin does not have the qualifications of Bitcoin that made it grow with such a big leap over time.

Bitcoin will continue to remain the king among other cryptocurrencies to attract more people to know the benefit of Bitcoin, because those that embraced the opportunity last year to purchased Bitcoin and hold till this month of December made huge amount of income from Bitcoin in this bullish season. This new ATH that happened few days ago contributed what makes some holders and investors to have confidence on Bitcoin, because they believe it will increase to a higher price in the nearest future, and for you to be part of the benefits in the bullish season you have to purchase Bitcoin from the market in the bearish season . Whenever the price of Bitcoin is increasing, other cryptocurrencies price will be increasing too, because it attract other cryptocurrencies teams to make their coins to increase along side with Bitcoin for their holders or investors to enjoy the benefits of their coins.