If I make ten games, and you make one, you could say I have a ten times greater chance of being published.
Sure, your one game might be better than the average of my games, but I still probably have a five times greater chance of being published. This doesn't mean I complete all these games. I abandon most of my games early on.
My great games have not come from some stroke of genius, but from a stroke of genius on top of a lucky choice of theme or mechanic. Each new game is another stab at greatness.
I'm increasingly convinced that most great games were not made by amazing designers, but were flukes created by reasonable designers. I've seen designers of some of my favourite games go on to make numerous mediocre and flawed games.
If you only ever make one game, you'll never make a great game.
There's so much that needs to be learned, and it can only come from a variety of experiences, successes, problems, and failures. Spending all your time on one game doesn't give you that necessary experience. Even if you did become an excellent designer later on in the development of your game, it would be too late to apply this knowledge to the important early choices you made for your game.
If you made a second game, would it be better than your first game?
When I look back at my early failed prototypes, I can see mistakes in them, that I couldn't see at the time. You'll be able to do the same thing, too. However, for now, the only way you'll avoid these pitfalls is by trying multiple games. My earlier successful games were just the lucky ones, that avoided the pitfalls.
I made a pirate game. I put a lot of time into it. I couldn't get it published. Was it a bad game? No. Was it about pirates? Yes. I didn't realise how hard it was going to be to get a game with no new theme or mechanics published. So, it went back to my shelf.
A friend spent years making a game clearly evoking the Power Rangers, in everything but name. While we were working on the game, the company that owned the IP suddenly announced a series of Power Rangers board games.
I've seen many people's "masterpieces", and just thought to myself "clearly this isn't going to work", or "There's really no audience for this." That person might be you.
Some people seem to think that the way a great game is made is by working an idea endlessly, until it's great, and that anyone can make a successful game.
When I play another designer's game, I rarely quibble with the details. The game has huge issues, that the designer is completely blind to. Even if it's good, the game needs major structural work. Other games are feeble, and unsalvageable.
Even if you don't make any mistakes, it doesn't mean your game is great. The central idea of the game might just not be that good.
There are so many mistakes and misfortunes that can befall you, that a single game has a good chance of being doomed, due to outside circumstances, or due to flaws you cannot see or understand.
Make lots of games.