Getting murdered by inanimate objects has proven to be a successful formula -- just look at all the sequels for The Omen and Final Destination -- but Death Spa is unique in that it requires people to be inside a 1980s health club to be in any sort of danger. This is a somewhat limited pool to draw from, and once word got around that people were getting killed by the exercise equipment, we imagine the membership fees would dry up.
You can understand the brilliance of great films by watching terrible ones; for instance, here you suddenly understand that whole plot point in Jaws about how the town depended on tourism and intentionally gave beachgoers a false sense of security about the shark. Otherwise the audience is going, "Damn, can't these people just not go swimming for a while?" We dare say that Death Spa did not put as much thought into it. Beyond pointing out the obvious fact that a butterfly press cannot possibly kill someone the way it does in the film, no matter how much weight you put on it ...
Seriously, it can't pivot back beyond its own fulcrum. Read a book.
... what's to stop people from just not going in? Couldn't the people of the 1980s exercise at home, or at the YMCA, or at any number of other non-possessed spas and rec centers, with absolutely zero chance of getting drowned in the lap pool by a ghost? The Death Spa would claim one, maybe two victims before everyone in the city decided to never go near the place ever again and just sit on the couch eating diet pills in front of a Knots Landing marathon.