Officially, there is a rematch clause:
Deontay Wilder Has 30 Days To Exercise Clause For Fury Trilogy
There is a contractual clause for a trilogy fight - and Wilder has 30 days to exercise that clause - with the contest taking place in June or July.
https://www.boxingscene.com/deontay-wilder-30-days-exercise-clause-fury-trilogy--147028So Wilder has a month to decide whether he wanted another part of Fury or not.
Regarding the gate attendance of the fight, it broke heavyweight records in Las Vegas
By the time they entered the ring Saturday night, MGM Grand Garden Arena was packed to capacity. Officials announced a sellout crowd of 15,816 and an MGM Resorts International official confirmed that the live gate for Wilder-Fury II broke the Nevada record for a heavyweight fight.
https://www.boxingscene.com/wilder-fury-rematch-broke-heavyweight-gate-record-vegas--147020So there could be more money in a trilogy, Fury is a good seller and so is Wilder, and they could potentially earn more than the second fight.