Okay, this is going to sound REALLY simple and basic but...

A couple of things:

First, you could simply be draining them. You mentioned they were fine for a blow job but that was it. Well, maybe, that is all they have to give? Sure, some guys can continue after they are drained but alot of guys can't and not only that... you are giving them what they want so why should they continue? Okay okay, submissive nature and all (and, trust me, I do have one) sometimes it takes a little effort and creativity... and determination to make things last. Someone once told me... it's easy to make a man cum but the real challenge is to make him last. Maybe, you need to hold off a little bit. I am not saying deny the man I am saying make the pleasure last. Read some articles and books on tantric sex, it might help. I mean, most men are good for their one cum and that's it and it takes awhile for them to refuel. (Not all but most.)

Second, as others mentioned, communication is a big part of it. Find out what else they like or are into (besides blow jobs) and let them know what you are into (besides giving blow jobs). Use the list on the forum the others were talking about. It's a good list and great fun if you use it with someone. And, it really opens people's eyes to how many things are out there left to be discovered and explored. Don't just get on your hands and knees and open your mouth... open your mouth long before you get on your hands and knees and I bet you will have better results.

Thirdly and lastly, expressing your desires is not a form of dominance or topping. Manipulating to get those desires fulfilled is. Don't settle for someone that you have to manipulate. Settle for someone that WANTS you to get just as much pleasure out of it as he does. Be picky. Make a list of your desires and limits (not just so that he can be more aware of them but so that you can also know what you want). Another wise person said to me... if you don't know what you want how do you expect to find it? Know what you want, don't settle for less.