It's a real pain to get them right and very few builders want to take the risk. Big companies don't care if they have to eat a few frames because the press fit bb is bad. And they have the market power to just ignore customers that have problems with them, if the internet is to be believed. No small builder has that luxury. Seems like there was a time when someone offered a reamer/facer for a press fit bb, but a number of people got burned in that deal.
I have been doing a lot of frame prep recently and i was thinking about how you could do it with machine tools. I think I have heard of people using boring bars on a mill for press fit bb. Fixturing would be an issue, but it is doable