Looking in the CK2 files for special events during battle and years, they have a tier system. Each month or year, there's a chance to proc the event, but each separate event also has its chance modified or canceled by additional traits and requirements. The list can be pretty long, average by about 12 per event.
This seems to be a way to produce random events in CK2, For Stellaris, the UI probably can't include all the variables they scripted in.
Yes, that's an interesting point. On the moment (I had to think fast because the devs were there) I essentially thought to the EU4 diplomacy tooltips.
Although, if such a system was implemented, maybe dispatching the modifiers between categories (e.g. "Permanent modifiers", "Temporary modifers", "Current technologies"...) would help having a better understanding of what makes a tech more or less probable to be available again?