^^With Bradley I believe team Khan at first offered Bradley no PPV money but because Bradley kept saying no team khan kept upping and upping his purse, to finally where it was 50/50 on everything. It was an amazing deal for Bradley, much, much more then he deserved and he still turned it down.
The reason that fight was so important was because Bradley was the #1 fighter and Khan #2. It would have been a unification bout, The Ring belt would have been on the line and most of all it would have recognized a true champion at 140 pounds.
Judah was a back up plan so naturally he gets less. He does have the IBF title but he's only ranked #6 overall in the division according to The Ring.
I believe Kathy Duva is Judah's promoter so it was on her if she couldn't negotiate any of the UK PPV. Or like Naner said, it could have been a "take it or leave it" type deal offered from Khan where Judah didn't have any room for negotiating, and if that's the case he's still better off taking it because the money he'll get from HBO is more money he'd get from anyone else in the division.