The Prius is a reliable, well built car backed by a company that has an extensive and easily accessible dealership network; it's effectively the opposite of Tesla in some regards (namely, service). In addition, a Prius is pretty efficient, low in pollution, and a good value for commuting, especially if your commute is less highway and more city driving, and for these reasons they are popular.
Teslas, on the other hand, overlap a few of these traits (an electric car by means of being electrically powered does not produce emissions itself), but there are far more reasons to buy a Tesla and not everyones' are the same. For instance, I bought a Tesla because I wanted the fresh bleeding-edge tech that's so new it hasn't even been fully tested yet (for better or for worse), and the performance (in relation to comparable ICE cars in its price range). Whereas I do care about the environment, I do reduce, re-use, and recycle etc, this doesn't affect my car purchasing - I'm a "car guy", I've had V10s as my daily driver before.
I think this is why there's such a disconnect on this thread, as for some people a Prius suits their needs maybe even better than a Tesla. To others, it seems like a mistake as it satisfies none of the reasons they bought one.