Value. It has its own section as it's so important.
If players don't value your game, if they don't feel you value it, if they don't feel it's well done and trust it, you probably cannot monetise.
What provides value?
Lots of content. Lots of well-made content. Richness of the game.
You need to treat your merchandise as actual goods. You need to aim for high production values.
You can even think that instead of your goal being to monetise, you aim to provide methods and ways for the player to enjoy your game. Even further, you might be providing help.