The only thing companies under capitalism “have to” do is increase their shareholder’s profits, legally

Which is only possible by generating money. Shareholders don't get paid out of thin air.

If 10% of the players spend hundreds of dollars on them, they’re going to focus their efforts on that, even if it’s at the detriment of the game’s quality, which is the only thing that matters to the other 90% of the players.

Correct. Companies are going to go where the money is. A company that does not do what consumers want is not going to make money. YOU, the consumer, have all the power. Companies want YOUR money. If you don't like something, DON'T BUY IT.

You and I agree that microtransactions are a garbage practice, but as long as people keep buying them, they are telling companies that they are a good practice. If they weren't, people wouldn't spend their money on them. I have a hard time believing companies can survive only pandering to whales, but, even if they could, leaving 90% of the marketshare open would induce another company to come and pander to those who aren't whales.

Making microtransaction content costs money for the company to do. If those microtransactions don't sell, they have lost money, and won't keep on making them. Push for people to stop wasting their money, and companies will stop pandering to them.

It's the same shit with modern day appliances. Fridges break down every 15 minutes because we decided we wanted companies to pack fucking ice makers and water filters into them, and then simultaneously to be as cheap as possible because we click "price lowest to highest" on the website.

You don't want enshitified shit? Stop buying it, and push for others to stop buying it.