Vegas paid 500M and Seattle paid 650M for a franchise , they didn't pay those prices to toil at the bottom of the standings the way every expansion team that came before them did.
The rules were rigged so that they would be competitive in short order. Vegas , because they came 1st , had GM's overreacting and giving up way more than they should, so that explains them. GM's learned from that and didn't repeat the nonsense when it was Seattle's turn., that explains why they were slightly less successful.
None the less with 30 teams to chose from your going to get some good players plus high end draft picks don't hurt either. It used to be that teams could protect 9 forwards , 5 defensemen and 2 goalies, do you think either Vegas or Seattle would have been successful if they had drafted by those rules? Not a chance . Nor would GM's have been overreacting and giving away way more than they should with those rules.
Follow the dollar, it explains any question you might have. 60 teams in 10 years? I really don't see that.