It's fine to explain why it is the way it is, but at the end of the day that's still just an engineering problem you need to try and solve. Sometimes Apple made mis-steps in that size/heat scenario but they've done it a hell of a lot better than anyone else for a long time. Sometimes you need demanding product types to force you to put serious effort into an engineering challenge you don't deem worthwhile.

There aren't a lot of phones that have air vents, except for the ones that also have fans. Convection doesn't work at those sizes and power levels. Thermal design for phones is all about conduction, getting the heat out to the surface of the device and spread evenly enough that there's no hotspot that would be uncomfortable for the user holding the device.

Some phones have fans??

In an alternate world where your phone has a Core i7

There are phones made specifically for gaming, and some of them have fans.

No idea, but technically some phones are now water-cooled.

I have seen reviews of redmagic and asus gaming phones with fans.