This is interesting, it seems like Nintendo chose the MOST unlikely pokemon to get their new type of evolution. If you look up Crobat in the online pokedex, it says that Crobat's name is a mixture of "cross"(as in angry, upset, UN-happy, etc.) and "bat", so you need to make the "ghoul bat"(Golbat) happy to make it a "cross bat"(Crobat)...
To me, this seems totally illogical.