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.
I should try this. We recently moved, and now have a gas stove, the over heats up INSANELY fast and I swear food cooks faster in it even with the fan off (Is there some humidity factor?).
This was so uncanny I did some direct comparisons with the oven in our old house (Went back to clean it up for a weekend). And it actually cooks things faster, after preheat. Literally no idea why.
It's probably just a higher end appliance. After growing up with my family only ever getting used ovens and replacing with more used ovens when they broke, I finally tried a more expensive new unit and it was an induction stovetop with convection oven and it's unreal how different it is. I still use the air fryer pot lid for various things though.
Gas (UK) delivers heat much faster than electric does. This is part of our problem in changing over from "conventional" fuels to electric, and the reason why I remember my mother's gas eye level grill so fondly. Cheese on toast under a gas grill was so much better than you can ever do under an electric one.
Recent fan ovens help, but you're still limited to the amount of KW compared with the insane calorific value of fossil fuels per unit of volume.
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.