On top of that I think most US players play on iPoker skins (black chip poker, cake poker, etc.) which allow US players.
But yeah, all of them (apart from the Nevada/New Jersey sites) are technically illegal down there. Most professionals who didn't quit poker altogether and didn't transition to live either moved to Canada or some third world country with no taxes and cheap living to grind.
I played professionally a few years back, so this was my understanding of the law then, and I haven't heard of any changes:
It's perfectly legal, as a player, to play. Laws have been created that prevent banks from transferring money to and from poker sites.
When Black Friday happened, it was primarily because poker sites were committing fraud to work with banks to process payments.
There are still sites operating, however they take very, very long to process payments, limit cashouts to a point where professional play is not possible, and can suffer the same fate as the big three sites did on Black Friday.
All of my professional-playing friends quit or moved out of country after Black Friday.
You can bypass location restrictions with VPN, but you also need a foreign bank account and can be caught and have your funds seized.