Regardless of what the skill is, some people learn faster than others. Their favorite abstractions and conceptualizations, that they use every day and for everything, are by chance very effective for learning that skill.
Also other advantages like great memory.
As for factors that are more easily observed, vital are youth and passion. The average player has neither of these lol :)
More tools like videos and books are nice, but it's easy to use them in ineffective ways. Still, I assume the average player today is better than the average player 100 years ago.
Consensus here seems to be that an ordinary person without talent can maybe reach 2000. Most believe that an ordinary person can't become a master. And almost everyone believes that an ordinary person can't become a grandmaster.
This is subjective but I think this is what majority believes from my experience on this forum. I am not counting opinions of those who intend to become a grandmaster in a year after they learn the rules.
What I wonder is, how did some players from history become great at chess even though ordinary people today can't?
Did they have so much more talent, that ordinary person today could not approach their level, even though they didn't have so many books, modern chess theory, computer analysis, annotated grandmaster games, chess puzzles, strong coaches, computers to play against, nearly as many opponents as we can have today and much less strong opponents?