I'm going to go out on a limb here and say that part of what MB doesn't mention about why MiB II failed while MiB succeeded was that MiB was sort of...
Realistic isn't the right word. But it had a kind of internal logic permeating it that made the audience okay with going along with its world. There was plenty of funny stuff, but one rarely got the impression that the funny stuff existed solely for the sake of being used as a gag; rather, the strange, off-kilter and amusing things were just our reactions to a world that happened to work this way, contrary to (and sometimes parallel to in equally surprising ways) our own.
Around the point MiB II had Rip Torn kicking the bad guy in the face in mid-air fifty times in a row, I said, "Oh, hell. This isn't going to work at all, is it?"
So, I'm sorry (though admittedly not surprised) to hear that MiB III couldn't get its head out of its posterior. I think it would be possible to make another good MiB movie, but the series banks too much on Will Smith's charisma to make a reboot plausible, so... Sorry, MiB, been nice knowin' ya.