Just curious why you think they were not successful? They may not have many number one songs -- not their thing -- but I consider them one of the most successful 1960's band that survives to this day.
And they were not about money nor really into the business side of things, so the fact that they are not billionaires is probably meaningless to them.
If i were able to spend my life being an icon, having gifts showered on me, spending all day doing what I love most, playing music I would consider my life successful. At some point after they dismantled the wall of sound, they are pretty much free to do what they wanted, when they wanted - which was to play the music for us fans. I always felt the fame and fortunes were secondary, and actually unwanted by some (from many accounts, being an icon is what caused Jerry to over-indulge in dangerous substances which were just too much for him).
Plus so many side projects, Jerry's art, Mickeys work with world music, Bobby's children book with his sister Wendy, work with SEVA, the REX foundation, the rainforest charity work and on and on.....(I'm just scratching the surface here).
Obviously there is a dark side too...... Just look at Pigpen, Brent, Jerry, Keith (well Keith was a real accident.....the other's partied a bit too hardy).
But even today, even without Jerry, most shows sell out rather quickly (from what I have seen, this was the first tour I recall where they didn't sell out every venue - at least on the east coast).
And they were obviously not sell outs. Not too many top 20 hits (ok touch of grey, throwing stones) and not to many cheezie songs (maybe dayjob, dough knees me in ...)
FFF! Family is Forever!!!
May God bless and keep you always
May your wishes all come true
May you always do for others
And let others do for you