I think it is most likely inexperience compounded by some Domme sites that expressly tell prospective clients to keep their emails very brief. The inexperience makes it difficult for them to succinctly provide the kind of information and feedback you prefer and their fear of angering the Domme intimidates them from writing longer emails that might provide you with the info you want.

Hopefully over time we all learn to simply and clearly communicate our desires and needs in a session because that's where great session experiences begin.