Yes but…

We’d pretty much seen it all before.

I mean the Graboids, Shriekers and Assblasters had all been featured in the previous movies.

That really left only the Mixmaster monsters.

Really, I think that it was simply that the premise was thin, and just ran out of steam quickly.

But then again, who knows. Highlander managed to get four movies, and three television series out of chopping off peoples heads.