Apols - for clarity, I'm not suggesting that a blind eye is turned towards safety. Far from it. But you can only do so much. You can ask people, and then tell them, and then instruct them using the delegated authority of the commander etc. etc. but after that, not much.
If I have complied with the regulatory requirements and done so repeatedly, courteously and intelligently, then I have done my job correctly. It may be possible to stop taxying, and at larger airfields it may not. Or you may get a flight crew who for some valid reason are unable to stop at that time. By the time that they can stop, it is usually too late.
I have frequently experienced all the situations mentioned in the OP. These are the same people who evacuate with handbaggage and on the way home overtake on hump backed bridges while not wearing seat belts. Normally, Darwinian theory keeps them from being able to reproduce, but not always.
Cabin crew don't (as was suggested in the OP) ignore the rule breakers (at least most don't) it's just that we can do no more.