I'm not sure a high temperature oven with a convection fan can truly be "buy it for life", the fan is going to die eventually, it's got a lifespan built in by physics. No form of maintenance-free lubrication or magnetic bearing is going to be able to survive such extreme temperatures for very long. As far as I know they're usually built on sacrificial bearings. Without frequent replacement or maintenance it's just not practical to keep the moving parts moving forever, and nobody wants to do regular oil changes on their oven or dig into its guts to replace a fan. Should we? Maybe. But I'm not sure if anyone is even attempting to cater to that market.

In general, the more expensive the appliance and the more significant of an installation it requires, the more likely people will go to more extensive lengths to repair it. From that point of view, a proper convection oven is likely to be more repairable than a small desktop air fryer. You can get an appliance technician to come to your house to replace the fan on your convection oven, not so much on an air fryer. And at the end of the day, they're pretty close to the same thing. Just one is bigger and more repairable. You might need to adapt recipes a bit.