This is not the headline you want neighbors to be reading about you while you are laid up in a body cast. In fact, this sort of accident is pretty unlikely to happen.
We still have to wonder why some home remodelers would risk it. See the photo below? This is an example (not the first one we’ve seen) of knucklehead remodeling. We are standing below a second floor bath looking up. What we see is that a previous bath remodeler cut out structural support under the bath tub to make room for new plumbing. The mid section of the tub was propped up by one wimpy 2×4 (instead of a 2×12 joist) and the tub perimeter was teetering on stacked 2×4 blocks. Really? You call this framing?
Our carpenters discovered these eccentricities when they removed the floor in preparation for remodeling that same bath. They responded by cutting out the ceiling below so they could get in there to install the correct structural support along with the new plumbing (see photo below).
Rock solid structure will stand the test of time and a lot of punishment. It ensures the sub floor won’t shift and cause cracks in the tile floor. The pipes won’t wiggle loose and spring leaks at the joints. Best of all, the likelihood of the tub dropping out from under you during your moment of zen is pretty much zero.