Why commercial gummies do not melt?
I've been making a lot of room temp gelatins lately; not gummybears, something else with a bit lower gelatin concentration. The secret ingredient seems to be time. The first day, things are pretty jiggly, but even when hermetically sealed, things get tougher and tougher over a course of about three to four days. I expect it's some colloid maturation process involving random chains finding their best fit over time. Don't quote me on that, but the same sort of thing commonly happens on a faster timescale with gluten  maturation in bread dough.
A few hours in the fridge can speed up firming, but I'm not sure you end up with the same final gel structure that way.