Earlier quoted context omitted.
If someone really wants to run they can still do so, but the story you hear from everybody who does it is that it's not worth it. You spend the rest of your life looking over your shoulder and working petty jobs for cash and living in squalor because the nice places check ID. You also can't contact friends and family anymore. It's a sucky life.
I suspect Whitey Bulger preferred being on the run to the alternative. If someone decides "it's not worth it" and wants to stop running, all they need to do is turn themselves in. Their revealed preferences suggest that they prefer being on the run.
The miserable life of being on the run might not have been worth the original threat being faced, but, regrettably, it may be worth the original threat + the new threat.
That's why every so often governments will have amnesty-like programs where you are able to turn yourself in with no extra consequences if you have a warrant. Or, for that matter, register for citizenship or legal status without fear of facing the legal consequences for the original illegal entry or overstay of visa.