well, cant say your wrong X3

That's a pretty bad way of thinking, artists have no choice if they have more demand than they can supply. They don't get to choose to have a large following. You should still commission and support them

Most popular artists rely on a raffle system, where everyone submits their ideas and then they choose what they'd like best to draw. If you're not actively applying for a commission then it will be quite hard to get one. Usually if you apply enough times you'll be recognized and eventually chosen

Aaaaww Even though ya, it's not the end of the world it can still feel pretty frustrating and disappointing when this happens :\

Have you tried just reaching out to them and asking them directly? I find that sometimes this can work and be a good way to get a slot as long as you're polite and don't flood/pester them with a bunch of message.

Asking never hurts!