I know most fiction works like this, so its understandably tempting to make one character the main character in the campaign. However, it doesn’t work like that in practice. Your audience consists of a handful people in the form of your players. Each of them has a character and each of them feels particularly close to that character. So, for them, your chosen protagonist is just a nuisance that keeps their character from taking the spotlight. Nice job alienating most of your audience.

Not all characters need equal time, but that shouldn’t be up to you as the GM. You should give chances for equal time for each character. It should be up to the player how they actually use that time. Yes, this might mean that some characters rise above others in importance objectively, but subjectively, each player will always have a special place in their heart for their own character.

And its just not player attitudes that’s the problem. I don’t get to play much these days. Every RPG session is a huge hassle that requires quite a bit of forward planning to get together. Adults have all sorts of obligations that might require them to step away from the game for a session or two. So, why would you risk putting so much importance to a character that might not even be available for long periods every now and then.

I’m all for putting the spotlight on one character during one session, but these spotlights should be handed out equally. This doesn’t leave you in trouble if that one special character is away for whatever reason. This also means your campaign won’t get stale when you can use each characters peculiarities to base your sessions on. (I don’t really plan the sessions. I usually just plan one opening scene starring one of the characters and let nature take its course from there.)

I understand that some people will instinctively move into a more supporting role in the campaign, but again, this shouldn’t be your decision as the GM. Let them find their place. Nudge them to take part more actively sometimes and, if they do, fine. If they don’t, that’s fine as well. For some people games are only about hanging with their friends. Still, and I’m going to say this again, the decision isn’t yours. Leave it to the players. Its good to recognize the decisions they come to, but assume as little as possible. Just because someone took on a more side character role once doesn’t mean they’ll always want to do that. I know I’ve taken on plenty of different roles within the group. If I’ve had (or taken) that freedom, why shouldn’t others have it as well?