Looking at this from just a person's standpoint, yes, some of these moves make no sense. But, looking at this from another point, it does. Mew learns each and every TM and is considered the mother of all Pokemon. If all Pokemon did come from Mew, it would make sense if they know some TM moves that seem weird. It shows how they're related to each other. Relicanth is a Rock type but probably came from a Rock-Ground type before and ekpt its ability to perform Earthquake.

Besides, several of these strange moves make the 'non-cute' Pokemon more powerful (Stantler, Tauros, Dusclops, Dunsparce)