For them to respond to foreplay by doing some of her own. Then maybe move on to some mutual oral sex (69 or otherwise). Then she get on top straddling me wide, and maybe a little doggie style session before I take her down and climb on top and lay deep meat to her.
Male ego mostly. They think they need to try and get deeper in you to please you and get you all worked up to make you ejaculate. They may be watching too many porn movies that depict such action as well. Also, self gratification. If they feel hot and ready to spurt, they normally and naturally...
Well, you definitely want to wait until after a few dates, so you can get to know him a bit and see how he respects you under normal conditions. Respect comes from not only what you do but also from who you appear to be.