Fox has a deal with HBO which doesn't expire until 2022. Dark Phoenix has aired on HBO, not Hulu or Disney+. Neither has Call of the Wild - a Fox kids' movie which Disney could have easily rushed to Disney+ for additional content back in March. It hasn't aired on HBO yet, still is in theaters overseas and but is available on VOD.
The question I've heard on whether the HBO contract is an issue is if Disney does skip a theatrical release, the HBO contract might not apply since HBO wouldn't want to be stuck with Fox movies which were so bad the studio wouldn't release them. When that contract was written, there never would have been the assumption something like this would happen. Instead, it would be HBO not wanting to be forced to air bad movies. Those types of deals frequently include some level of box office performance since that's used as a gauge of quality & interest.