While I suspect it probably mostly happen in cheap, touristy guest-houses, you can’t discount the fact that this is Thailand. And, in Thailand, safety is not necessarily the utmost importance.
Knowing that people have lost their lives from innocently taking a shower sent shivers down my spine. I don’t think this is something that we consciously think about (tourists or not), but it exists and it is very real.
It makes me wonder if there are some sensible way to gauge when safety in the shower is being compromised.