Writer's Fallout Shelter

I have, both in fiction and non-fiction markets - mostly paying markets. I've been accepted and rejected (is anyone who actively submits work accepted all the time?)

It didn't seem like a "leap" at the time.

The question is, why don't I submit work on a regular basis? What is it about the process that holds me back? Impatience. I don't mind rejection, but it takes too long to write and rewrite for me to be satisfied waiting 6-8 weeks, let alone up to 4-6 months, for approval or rejection (and payment) - especially when most markets clearly say "no simultaneous submissions" and "no previously published work." Blech.