Where are the precursor tablets?

Being the core pillar of the endgame, precursor tablets are so rare I have seen more unique drops than precursor tablets.

Why are they so rare? Am I not farming the right places? Is there a certain place where they drop more?

I thought the +30% quantity of precursor tablets was going to change it, but it doesn't. I'm still constantly looking for them and staring at empty towers and swatches of unjuiced nodes waiting for tablets.

Endgame feels like I'm supposed to explore 3 regions and would have probably enough tablets to juice up only 1 of those regions, and the other 2 regions should just be abandoned because they aren't getting tablets so they are a waste of time to run. Is this the expected experience?

Where are all the precursor tablets?