Well it's not anything the provider does or doesn't do. Partly it's age and drugs I take for medical condtion. I can cum more easily with a lubed hand job, but I'm only good for one shot, which if at end of session or late at night, if I could fall asleep, would be OK, but I often get a bit depressed after cumming called post coital dysphoria (some women do too).
So, it's more fun to have an erection and it feels good to stroke the insides of a young, good looker's vagina with my penis, especially if she also feels good. Sex is best when both of us are mutually into it.