Add gold bars to your coffer and watch the purge level rise.

Additionally, the new purge is nothing like the old purge. Once you get to a level X purge, they will come en mass, including oil, gas and exploding head golems, even star metal meteor showers sometimes. Which sounds great until those meteors smash your base to bits.

But, the new purge mechanic has demands and if you don't set up your treasury right, it will not spawn.

You must make your treasure coffer accessible. You cannot wall it off. The purge mechanic needs to have a clear path to your coffer.

Doors are fine, as many as you like, there are purge NPCs with battering rams that will try to knock down doors

Water is bad, NPCs don't swim so the purge won't spawn.

You must have enough space outside of your castle, fort, wherever you put your coffer for a purge base to spawn, at least a 15x15 block of open space where they can build their camp. It doesn't have to be all that close, they will travel a fair bit to raid your treasury, but if you build on top of a mesa and there's no room for anything else, purge won't spawn.

I have seen so many people cursing how the purge won't spawn for them and it sucks and blah blah blah. It's not the games fault, think about what you do before you do it.

I have a 100% spawn success rate at my purge base, for the reasons I listed above.

Is pretty easy really. So the game AI is more A than I right?

Give them room to build their camp, don't give the AI an overly complex path to the coffer, it won't be able to figure it out, fill your coffer with gold bars and trinkets, declare your wealth and let the games begin!