If you look over the history of MMORPGs, particularly 1st and 2nd gen MMORPGs, you'll find that to simply not be the case. Far from it. People play these MMOs for years despite having RNG, low drop rates and the like.
The problem with topics like these, and arguments like yours in particular, Endemerrin, is that they're made through tunnel-vision goggles and judge every situation in isolation instead of considering them as part of a bigger picture. No one sticks with a game, or leaves a game simply due to "this one issue" or "that one feature". It's not that absolute. It's a collection of things that keeps people playing, or pushes them away.
For just one example, Final Fantasy XI. They maintained a healthy, very loyal and dedicated player base who stuck with the game for 7 or more years, and XI was extremely dependent on RNG based rewards. More than that, it was based on RNG, on top of rare spawns with long periods of time between spawn windows. Still, people hung around, even well after MMO's like WoW and its ilk started popularizing the "casual friendly" route where everything comes easier and faster.
And the reason isn't because "all people really love RNG content", although some actually don't mind it at all because they enjoy the activity itself and it isn't about the reward for them. It's because on the whole, RNG was just one wart of several on a MMO experience that also had many benefits and things they enjoyed. The good balanced out the bad.
FFXIV has been RNG based for how long now? People have been stating "SE if you don't fix this NOW! people will leave!" for how long? I've seen this topic come up after every new Primal or other content that's implemented. And every time, those people are still around to repeat it for the next time around. Guaranteed they'll still be around for the next one as well.
Why? Not because they're masochists. It's because, as annoying as the RNG or low-drop rates are to people, there's still enough else about the game they enjoy that they'll continue playing. There are people on these forums right now that I've seen complaining about the same things going back for months. They've been making that threat that they and others will quit if SE doesn't do what they want. And yet they're still here. Still playing, and still making that threat. They'll be here months from now doing it as well, guaranteed.
Why will they still be here? Because despite the issues they make out to be "show-stoppers" for them, there's enough about the game they enjoy and that keeps them playing.
Some people just like to hear themselves talk, they love to be "right", and they love to use hyperbole or absolutes to make their arguments seem bigger or more important than they are.