Earlier quoted context omitted.
The fact that they have a ton of VC they're already beholden to that is here in the US, and who aren't interested in IRS scrutiny themselves.
Also, the fact that Coinbase is in the US legal jurisdiction gives its clients confidence they would be made whole if anything untoward were to happen.
If anything is actually protecting clients against crypto theft, it's the exchange's privately-purchased insurance rather than the government. Although I wouldn't rely on that for much either as insurers are rarely eager to pay out.