Where do you see that? Watching the documentary I see people who have been, for years, putting in the work. This is them going to work. Most people I know who have not met their songwriting goals do not put in the time, day after day, year after year.
...but plenty of people put in the work and never come up with anything close to what the Beatles could. Including, it's worth considering, any of the fab 4 in their solo careers. Sure, there were a few hits. But nothing comparable to the insane productivity from when they were a band.
So it looks to me like the formula is: hard work + talent + band chemistry = hit making machine. And only the hard work portion of that is within anyone's control.
There is an important component I think is necessary somewhere in there, maybe lumped under "talent:" and that is a link to the zeitgeist that would let them come up with popular content.
What if this band worked hard, was talented, worked great together, but had no idea of current events or what the currently popular music was to rebel against; and instead ended up cranking out baroque Bach-like classical pieces? I bet they would remain in obscurity.