Basically, the main reason is the fact that they can be. I also would like to point out that we feed their greed and that is causing a lot of trouble for the crypto world.
If we only invested into the top 20, and here and there decide which ones to be out of top 20 and new ones to get in, but do not invest into anything else, that means about 100 billion or so dollars would be going back into top 20, that would make the prices of everything go up insanely high, that’s like adding more than 10% to each of them and in a single move, and that would be a HUGE thing when the prices go up during the bull run. That’s why the devs do it, they can make money from people who still invest into shitcoins instead of top 20.
But you can't blame the millions of crypto enthusiast to trust their money to a person like SBF because at that time they are really doing good, even becoming the second largest crypto exchange behind Binance.
But there is a big story behind that we didn't know, until it was too late, no one see it coming maybe except SBF and his ex-gf and his CFO. Now the 3 have been indicted and hopefully all of them will go behind bars for the crimes that they have committed.