I think the lack of hype for Toy Story 4, in comparison to the previous Toy Story films, is a multi-layered issue.
On one hand you have the fact that, Toy Story aside, Pixar's sequels have had an air of "did this really need to exist" around them, and in general have not been as good as the films that came before them. Finding Dory, The Incredibles 2, Monsters University...all of them have had this trend. They tend to review well, but still feel like unnecessary additions that don't hold up to the originals. The only one that bucks this trend really is, oddly enough, Cars 3, but that's mainly because Cars 2 is widely considered Pixar's single worst movie, and even then Cars 3 got somewhat mixed reception.
It doesn't help that their non-sequel films after Toy Story 3 have been also kind of hit or miss. Inside Out and Coco became beloved instant classics, but Brave kind of got a somewhat middling reception among fans, and The Good Dinosaur is usually considered Pixar's worst film that isn't Cars 2.
But this is further bolstered by the fact that many consider Toy Story to have been the literal perfect trilogy. Given Pixar's recent trend of making sequels that aren't as good as the originals, this is understandably worrisome. People don't want the franchise tarnished. Add in the film's troubled production and this becomes even more apparent.
There's also the social media aspect. The fact that Detective Pikachu got so many more views on its trailer made Toy Story 4 an easy target for memes. Then there's also the fact that the teasers haven't really shown very much. We get to see three new characters, with Forky, Ducky, and Bunny, and we know Bo Peep is back, and that the toys go to a carnival and Buzz is taken as a prize, but beyond that there isn't much to talk about, as they've shown a total of maybe a minute and a half of footage between three teasers.
All of this together creates a sort of mood of apathy, but I have no doubt that will change as the film gets closer to release. Personally, I'm optimistic. I don't think Pixar would screw up their holy grail franchise that literally put them on the map.
