I worked a lot with and built up ultra-high vacuum systems during my PhD. At least for that level of vacuum, you introduce a lot of headache.

You can't use normal plastic or any kind of lubricant anymore because it starts degasing inside the vacuum, pump down after opening to air is a multi-day process that involves heating everything up to 150°C to get rid of the water that will settle on basically every surface when you pull the vacuum, every electricity feedthrough is a potential point of failure, transfering objects between different stages is a huge hassle etc. pp.

I'm sure there's still lots of UHV and HV systems in a chip fab, but there's no way that's easier on a full factory scale than clean room operation.