At some future point, if CBS All Access survives, it is all eventually going to end up there.Except they are not under the same roof - remember part of the financial model is selling the series to international streaming services - a show that relies on narrative from shows not on your service is less attractive and also contractually complex.
Section 31 is a spin-off of Discovery so Netflix has first rights on it. Picard is not so it can be openly sold.
It is pretty unlikely to me that when Amazon were doing their due diligence they did not ask "this does not rely on strong ties to the Netflix show?"
Cameos, easter eggs and references sure - that we find out that it is an bad guy from an entirely different show? No.
And with one guy running the whole shebang at this point, I see no problem with threads interconnecting the shows.