Just like they don't spend hundreds of millions of dollars trying to crush other competitors in this way. It would lead to criminal prosecutions, massive lawsuits and irrevocable damage to reputation.
JPM and other megabanks face lawsuits all the time. Didn't JPM recently pay a fine of $ 80 billion or something on that order of magnitude? It didn't hurt them one bit, since it's just the cost of doing business for them. They're expecting such fines anyway, so they make sure they have the cash to spend whenever the shit hits the fan.
And does it look like Jamie Dimon or Lloyd Blankfein cares about their reputation? Remember, these players are so well-connected in political and judicial circles that they're never going to jail anyway. At most their banks get some silly 100 billion dollar fine before continuing doing business as usual. It's nothing to them, and what reputation they do have isn't hurt the slightest by crushing something as small and insignificant as a cryptocurrency. And if it
is hurt, they don't care anyway. (Arguably, their reputation (among the common man) has already gone down the drain for the last five years or so. Yet, they continue doing business as usual.)
I want Bitcoin to succeed. That's why I hope someone can address the OP's points.
Yes, it's a game of whack-a-mole, since a dozen other cryptocurrencies pop up if the banksters decide to destroy BTC. But can cryptocurrency as a concept ever truly
succeed (i.e. achieve mainstream adoption) if it's just destroyed every time some serious financial player sees it as a threat?
Currently, BTC is tiny, so the megabanks lack incentive to destroy it. It's not a real threat to them yet.
But hey, I'm a newbie, so maybe I'm totally wrong. That'd be a relief for me.