Call me boring, but I like predictability. Once you've established a rapport with one or two regulars whom you know offer the services you want, why risk your fee on a stranger who, potentially, might not deliver? Also, as I like a submissive, I'm a bit limited to that cohort.
I fully appreciate a lot of guys want adventure and variety of the 'so many girls, so little time' variety, but it's just not me.
The danger, of course, is that you end up liking one too much. Did happen a few years back, but I didn't break my heart over it; just went out and found other good regulars.