Minor League Baseball teams still fold all the time. Nobody uses that as an baseball isn't stable argument. There will always be some volatility in the Minors. Soccer is going nowhere. Also MLS doesn't want to kill NASL, MLS wants to build a minor league system that touches all levels. If NASL would have participated in this there would be a relationship with them. Since they did not MLS has picked USL as their Minor League of choice.
Kinda wish they kept the flame, stands for "united rapid growth" lol.... with the whole MLS theme of the crest heres what should've been created.