I can see Apple viewing that as low priority given how easy it is to connect to an iPhone hotspot already. There are bigger opportunities to invest engineering effort into.
People on here have wanted Apple to put a cellular option on to their laptops for as long as I can remember. I know its easy to tether to an iPhone, but its also nice to have the native option like we get on iPads. Adding cellular would be another differentiator from the old to the new - but I agree its probably low priority for them.