Oftentimes places sell turbos that are from cool waters. The reason these snails die is because they are basically boiling to death in reef temps. Their metabolism goes into overdrive, which is partly why they have a reputation as such voracious eaters. But it drastically shortens their lifespan, in addition to being sort of cruel.
When I first started out, I bought three orange chestnut snails that turned out to be cool water species. They all croaked within weeks. I felt incredibly guilty, and this is why I always try to heavily research my purchases from now on.
If you are going to get larger Mexican turbos, go with the zebra kind: they are at least a little better suited to reef temps, though still not perfectly.