This tardive coining suggests a lack of a denominal verb directly from patria. Am I correct?
If so, why? Why wasn't there *patriare? It feels unnatural, outlandish (pun intended), and incomplete to have re + patriare but not *patriare?
Yes, I think you're correct. There is no Lat. denominal verb patriare that is directly formed from patria. As for the Engl. late verb patriate, it was coined from repatriate via a backformation process.
Why is there no originally unprefixed denominal verb like *patriare? Well, probably, for the same reason there is no denominal verb like, for example, *dentare (cf. edentare). That is, the reasons involved are probably not linguistic but encyclopaedic (for example, having patriam or dentes is what is naturally unmarked, so to speak). Linguistically speaking, there is no reason why one could not form unprefixed denominal locative verbs like patriare and dentare with the expected/corresponding meanings "provide X with patria" and "provide X with teeth", respectively. Cf. the existing unprefixed locative denominal verbs: humare ('to provide/cover X with earth'), marginare ('to provide X with a border'), terminare ('to provide X with bounds', i.e., 'set bounds'), etc.