Not everyone has a convection oven. They are portable convection ovens, not portable ovens.
I have a toaster oven because I don't need to heat my entire oven and use much more energy and time to heat the entire thing to reheat a slice of pizza.
I use the convection function when I'm working with large amounts but for 1-2 people, the air fryer is much faster.
Practically, things labeled "air fryer" make different tradeoffs than things labeled "convection ovens".
In particular, air fryers have comparatively big fans, and vent way, way more air out the back to keep humidity down, so they make food much crispier than a convection oven does.
Yeah, I keep trying to use my convection toaster oven as an air fryer and it doesn't work out and then I'm like "SEE?! AIR FRYERS ARE STUPID." But really I've never tried one.
But convection ovens aren't necessarily air fryers. To be fair though some air fryers I wouldn't even consider air fryers. If they can't turn something that already has a decent oil content to at least 60% of their deep fried version then it's just a piece of junk.