The mining category is missing when I select Build New Corp. The docs state the cap is 100 mining corps for an enterprise, I have no where near 100. Am I missing something?
I'm pretty sure the 100 cap is the total number of corps, not just mining corps. So your services and the likes are included. Best to build 100 mining corps first then move onto other types. It's an odd mechanic, I've no idea why it is this way.
You can actually build 109 mining corps. Get to 99 then queue up another 10 corps.
This is a known, but poorly documented function of the game. You might be able to get away with up to 118 IIRC according to some people, as long as you time the queued corps constantly until it takes the menu item away.
The 100 mining corps limit is introduced to allow all players to build such corporations. Mining corps are very profitable and countries or enterprises with many such corporations are doing very good and are very profitable.
allowing an enterprise to have many more such corporations will make it extremely profitable while others may not have the opportunity to build them.