all that seems noble and righteous, but unknown bands don't play big festivals.
you don't see unknown chefs in big hotel restaurants, you don't see unknown commanders leading big armies.
There are two perspectives you need to consider- The organizers, and the performers.
From the organizer's perspective:
First of all, it's an issue of reliability. Unknowns might have more quality than knowns, but they are not tried and tested. What will an unknown band do if say, the sound goes off? Will they get stagefright seeing more faces than ever before?
Maybe they can handle it, but maybe not. And it's easy to say "have faith" when we're not personally accountable, but as an organizer, you want to be as sure as possible that everything will work out well. What if that seemingly docile band suddenly decided to play some mindblowing heavy metal, yelled vulgarities at women and children and incited a riot?
Security comes in! People get arrested! People get hospitalized! Sponsors cry foul and remove funding, and next thing you know, LIME gives up on local music altogether!
You may say it wouldn't happen, but what if? There are no rooms for "what if's" in big festivals!
From the perspective of a gigging musician, it won't be the same if you just wrote a song and played it with a couple of people and BOOM you're headlining Baybeats or LSB! Overnight superstars. Chances are it'd get to your head and you'd blow up, somehow.
And even if you are humble as ever and pleasant about it, people will hate you. Loads of other musicians will whisper behind your back, "those guys didn't work for where they are at all, they probably sucked up to/slept with/bribed the organizers, they don't deserve a damn thing, etc". That's not very easy to deal with.
Unknowns can and should work their way up and earn their stripes! It's more meaningful that way too, in my opinion. The long hard road teaches you humility, respect, to take care of yourself and is really quite fun. Going through difficult situations toughens you up as a musician and a person, and you develop stronger relationships with your bandmates, etc. You learn how to deal with things, and you grow into your new role slowly instead of being dumped into the deep end.
just some food for thought, cheers!