Must be a combination of good money and length of deal. It's Roy's last chance to get a big pay day, so has to cash it in, not really all that surprising.
Best of luck to him.
I am 100% certain that it has. The Nix could've offered him a 5-year deal with big money too, but that's really no help if the club is only around for one more season. And then he'd be in the market again, but perhaps with a season that may not have gone as well for him as this one, and one year older.
His chances of staying here were never all that realistic, no matter how hard the club tried to retain him.