How do you know when it’s time to change MCs?

1- You would rather write the book about a different character
2- To make the book saleable you have to cut the characters that you feel are better and more alive than your MC so you can focus on the MC
3- You just can’t stand your MC anymore, you don’t fell she’s a viable character, etc.
4- Your tired of trying to sound like a 10 year old when you don’t know how to make a 10 year old sound believable.

Can you tell what I’m having issues with?