I feel like this topic is being somewhat romanticized.
I mean, can we all really say that we'd all only use our favorite characters even if it meant losing one thousand matches, or that we wouldn't even consider learning a different one even if it meant winning the same? Don't take this the wrong way, but as much as I have my favorite characters, I definitely wouldn't main a character that was too severely handicapped against top-tier opponents in competitive play. I'd still play them at all, but for a tourney or some other competitive reason, can we all really say that we'd all use a Megaman-ish character to get the job done?
Summary: With the amount and degree of "HELL NO" answers, are we all really being true to ourselves with these answers?
I don't know why you'd think we wouldn't.
The answer is that we don't drop mains because of tiers, not that we don't choose characters we think we're more likely to win with.
In Brawl, for example, I played my favorites and ones that just felt good/fun to play. This went up to 19 or so characters.
But when it was a serious match, and I was playing to win, I would switch to a smaller group of about 5-6 that I was confident I'd win as.
It's a situational thing. If you're playing to win money, you're going to switch to characters that you're more likely to win as, but that doesn't mean you have to sacrifice your favorites to do so. A lot of top tier characters are favorites anyway, and likeable characters.
My faves in Brawl span the entire tier list. The ones I played the most were top tier and bottom tier.
In SSB4, I haven't officially found my crew of faves yet, but I can guarantee it will be all over the tier list, from bottom to top. I'll play who I have fun as, even if I lose. Worst case scenario, switch to another fave that's better. Still playing someone like.
I don't support the idea of a single main, I feel like it limits you. Having options allows for you to experiment and still win with favorites. I don't have to choose them based on tier lists. Tier lists are based directly on players anyway, and they fluctuate like hell. You could have a first tier list with Ganondorf in the middle or moderately high, then have him drop. So you'd have to constantly change mains simply because a group of people say they're not good anymore or because someone else is winning as other characters.
The most sensible thing is to just stick to who you like, and then if worrying about actual tournaments, switch to the ones you like in higher tiers and focus on them.
So in no way do you have to stop playing favorites.
And even if you do play bottom tier the whole time, it's about having fun. If you have fun with that character, you're going to play them. And if you're playing for fun, and playing bottom tier, you're probably not really playing tournaments anyway outside of friends.