That’s a huge assumption you’re jumping to. I’ve spoken to people about GMing. Some have done it, but don’t want to do it again - they found it difficult, time consuming, and not as fun as playing. Others have never done it, and refuse to do it. Others have done it, and found they’re bad at it, to the extent that other players are reluctant to be in their games.
GMing is a skill, and not one everyone has. It’s not magic, and you get better with practice, but not everyone wants to. It would appear you’re fortunate enough to have numerous GMs in your local group, but as has been pointed out, that’s not the norm.