Why has Dark Thirst activated in my game?

[Bonesaw]

I get what it's for and is applied randomly but what have I done to have it activate to begin with?

[Starmachine24]

I think you get it from an upgrade from the contractor if i recall correctly

[Shadow Wolf]

Think you unlock it after getting 3+ weapons (so it doesn't just go back and forth)

You can upgrade it from the house contractor to darker thirst which applies its buff to gems as well but the original buff is not on there

[Manxome]

It activated for me almost immediately--I think after 2 escape attempts? But then it seemed to show up only for some runs; I suspect it was randomly falling on weapons that weren't visible yet some of the time. (It definitely sometimes selected weapons that were still locked, and at that point some weapons weren't even visible as unlockables yet.)

Might be based on reaching Asphodel or Elysium--IIRC I died to Megaera on my very first run, but then made it into Elysium in my second. Or it might just be based on number of escape attempts. Or maybe it starts immediately but you just might not notice right away if it randomly selects weapons that you can't see yet.

It doesn't require unlocking 3 weapons; I saw it with only sword + bow unlocked.

It doesn't require a renovation from the house contractor, although later on there is a renovation to upgrade it and make it apply to gems as well as darkness.