I'm not too sure why he keeps reinforcing the idea that "spells just happen". It feels like it's trying to dispel a common misconception, but I have absolutely no idea what that misconception would be.
KOTT's frames most of his videos as introductions to the game. He's doing "Pathfinder 2e for Dummies for YouTube". He keeps reinforcing the idea that spells just happen because it's the kind of distinction that someone who's never touched a TTRPG before might need made for them.
He does it over and over again because he doesn't assume anyone has watched any of his previous videos.
compared to lifting a boulder or leaping a chasm, you have to roll a d20 for those, spells just happen without rolling to see whether it will happen.
Ok first, awesome username.
But uhh, doesn't that same logic apply to a bunch of things? You don't roll to speak, you just do it (and roll to see if it was convincing). You don't roll to loose an arrow, you just do it (and roll to see if you hit).