Trumps own administration and DOJ already determined that it was a crime. It just took this long for it to work through the system to snag the mob boss, too.
But it's not the hush money that's the problem, it's how that payment, the other "hush payments" made before it, and the $420,000 paid to Trump's lawyer for it was accounted for, and reported on taxes.
This really is just the last piece in a big puzzle, and the least interesting or concerning thing Trump is being investigated for.