First, I never said that it was a good thing, only that Halloween isn't the only movie franchise to do so.
Second, horror films, especially those of the slasher sub-genre, are almost always treated as the bastard illegitimate children of the distribution/production companies. They despise the movies themselves, but love the high revenues they generate. So they're always hoping to permanently kill off the villain in every film, but then always want to go back to the well one more time after the BO receipts are added up.
Third, regardless of the nostalgia you feel towards Parts 4 through 6, they are the three worst films of the series, with inferior writing and acting in comparison to Parts 1, 2, and H:20. And while H:20 might not be quite up to par with the first two, it at least attempted to recapture the magic of the original so I have to give them props for that.
And finally, please don't even mention Resurrection. That movie shouldn't even have Halloween in the title. Hell, after H:20, it never even should have been made. The ONLY thing about that film I even REMOTELY liked was trying to spot Vancouver landmarks throughout the film.