D&D clerics implicitly are formally-inducted parts of religious organizations before they get magic, but this contradicts the sort of holy people they are based on. St. Francis of Assisi wasn't part of the Catholic Church when God called him and he started acting wacky, and he could fly (Catherine of Siena, who could also fly, was never formally adopted by the Church). Sufi mystics aren't mullahs. Moses and Jesus weren't rabbis or priests.

The job of a priest, sacristan, etc, is fundamentally different from a holy person who goes around performing miracles all the time. If you're a priest, your job is basically to make sure God or the gods aren't mad at the population, which tends to boil down to ritual and rules. Miracle-workers, on the other hand, tend to be outsiders, since you don't need miracles to appeal to tradition; an outsider is more willing to shake things up, but needs something to prove God (or the gods) are on his/her side.

Also, the flavor of being chosen by a god to do their work is more interesting than being the one millionth temple-adopted orphan.

Yes but i shant, for the tyrannosaurus is a gentle and noble creature made by Our Lord and deserves love and respect