It's odd - Avatar fans must live online, but there seems to be no online presence for that franchise. But - four billion and counting. Maybe they talk quietly, or are happy/content? I'm going to see the new one.
I think it's a multitude of factors including all the ones listed above PLUS I think the average age group for movie product has matured past crap tie-in toys - but Hasbro won't stop making crap toys. Do people really want Shang-Chi with arm flinging action, or defintely-not-Black-Panther-Shuri with arm cannon? NO. The product itself has improved but the audience has moved on.
So then it becomes a self-fulfilling prophecy - movie toys don't sell but not bc Hasbro fucked up. Oh no! Then the media production timelines being squeezed from principal photography to release to sometimes less than a year means 3D product is racing to the retail shelf and can't get there early because it doesn't exist - and then it's inaccurate. And then it doesn't sell. Rinse, repeat.
It's a bad cycle that really got exacerbated by the COVID shipping delays, then the movie schedule shifting ALL over the place for every company/studio, then the overproduction of 2021/2022 (Hasbro at least).
And then - the Grogu of it all. The secrecy of Grogu worked out in the long run for merchandise sales because the audience formed a genuine connection to the *character* in real time, NOT having merchandise ahead of time. But now SECRECY means filmmakers/studios don't want to share anything when sharing is how movie tie-in product was so successful for DECADES.
It's really sad to me to see the state of tie-in merchandise these days. Hasbro, who wants all of my money, got so burned by media tie-in merch that now they are leaving surefire sellers unmade, and markets untapped.