It's probably more than they don't think of covid as an ongoing thing. Stuff like wearing masks or having lockdowns isn't a thing anymore. A lot of things being done to slow COVID have stopped and people feel like it's over.
That or the shot isn't covered by government programs anymore.
It was always going to be an annual shot like the flu. That annual flu shot is to combat something that was a pandemic as well. We might even get combo shots at some point.