It isn't the "thoughts and prayers" part by itself, it is the "thoughts and prayers" offered by politicians and then absolutely nothing else. Even Christians can find it hypocritical:

> "Prayer that doesn't lead to concrete action toward our brothers is a fruitless and incomplete prayer. [...] Prayer and action must always be profoundly united"

- Pope Francis. (grabbed from https://en.wikipedia.org/wiki/Thoughts_and_prayers)

Otherwise, that to many people the phrase has become synonymous with willful inaction is just collateral damage.

It doesn't even call out the hypocrisy of christians that don't support gun control. They can believe in other ways forward, like arming all kids with guns and having them practice lots of active shooter drills, or whatever, but it is the "it is not that bad, let's not worry about it" attitude that makes people angry. The original comment I was replying to talked about a "having a national dialogue on gun control", which simply hasn't happened.