I'd say it stays alive largely for the same reason that Speed Racer does: it was an early anime available to US audiences (probably other English-speaking countries as well, eventually) that lodged itself into the hearts and minds of youth in the 70s and early 80s.

I never watched Speed Racer as a kid, and so don't have any of that nostalgia. But I know many people who did watch Speed Racer who are just as excited about it today as I am about Voltron.