Some of the straight wall cartridge states have the 1.8" case length limit and some do not. It looks like Michigan and Indiana do have the 1.8 limit so the .444 is not allowed, but Ohio and Iowa do not and allow the .444. Even with the limit there are already plenty of other cartridges available that are perfectly suitable, no need to make another.
it is largely marketing , if it was just about killing deer we might all be running one caliber
Because Henry seems to be the only one with a rifle for it yet , I assume this is Henry trying to expand their market.
Henry also just released a 9mm carbine that uses Glock , smith or one other mag type basically a Ruger PC carbine with wood stocks
they are trying to do more than old style lever guns
they found people looking for different/maybe better will buy new rifles if they make new cartridge that do something a little better than another.
also no one seems to be interested in 357max as a cartridge although it would have made a lot of sense.