Can someone explain to me why the memory vaults dont have options despite clearing all objectives?

Third memory vault in a row where I completed every objective in every map in the influenced region, and the memory vault had one item to 'choose' from of negligible value. My understanding was you got more options completing the region objectives. And yes, I have been clearing objectives, getting that popup in every map.

Had two more now. Am I supposed to just open the vault as soon as I open the last map rather than running it?

I could be incorrect but I believe in order to get more options from the vault, you need to clear the map bosses each time, not just clear the objective. The maximum choices I've had when clearing the boss in each map was 3, missing one boss is 2, I believe if you skip the bosses altogether it's limited to 1 choice.