On a well traveled route over the weekend it is very common for people not to stop/ask. If you're working on it the assumption is you have it handled. Look a little befuddled or give a wave and people stop. But for the vast majority of cyclists around here a flat is no worry and the repeated stop/"you OK?" get a little annoying so few people bother. For the fraction of newbs who are totally unprepared it does serve a valuable lesson. Someone always stops to help eventually