It's true that Gold's Gym became the mecca of bodybuilding, then World Gym for a time. But Vince's Gym was, comparatively, a tiny place. It was never going to be some big place that could hold dozens of people at a time.
Also, it was in North Hollywood, close to Universal Studios. In the 1970s, it was quite the place for the movie/TV industries with guys like Erik Estrada being staples there. Vince also didn't care to follow the norm -- he just cared about having a gym and training people.
By all accounts, keeping a gym over for 50 years is better than what happens with most gyms. How long does the average "boutique" gym last -- 5 years, tops?
DAS