Why do some bands get away with STEALING an older band's name?

Worse even than that, why do the NAME-STEALERS usually end up with more success than their victims (i.e. the ones whose names they've STOLEN)? Classic example: NIRVANA. This is the only band with any rights to be called Nirvana:
[youtube=https://www.youtube.com/watch?v=dcf19K5QFqQ]