Since I too wonder why this has happened, I will make a guess.
One of the sticky points that UIGEA dealt with was the funding of terrorist groups, and it did it by forcing Draconian regulations and prohibitions on US citizens and Banks. Their thinking seems to be that poker players will fund folks intending to do harm to US institutions.
Since we in the US can not easily withdraw our funds from the few remaining poker sites
that still serve us, that thinking goes a few steps further to prevent us from p2p xfers to those outside the US, where these paranoid 'thinkers' believe the majority of terrorists exist.
With banking regulations over the years making it harder and harder to move money around in any/many ways, (the $10K limit when on vacation for example), someone somewhere is exerting pressure to clean up these last remaining loopholes in how much control the government uses to prevent unseen money handling. On the one hand they want to make money movement as transparent as possible, while on the other hand they create situations which foster sneaky money movements.
So, my guess involves some outside influence (DOJ?) suggesting that by thwarting p2p xfers, these sites will lesson the wrath that the US gov could bring to bear on these sites.
But it is just a guess.......