So, the Pillagers only spawns one time when you approach It, then, they won't spawn anymore after that, even if you're on the spawnable radius they need to spawn.

How to reproduce:

• Set the game to Hard. 
• Go to a Pillager Outpost.
• Eliminate the Pillagers that spawned. 
• Wait up on the radius needed for them to respawn. 

Expected result:

• The Pillagers should respawn.

What happens:

• The Pillagers won't respawn on that Outpost, even with a Highter Tick rate.

Leaving the Level.dat of the world and a video of proof. 

Update:

Tested It on some Newly-created worlds, It's still happening, the Outposts spawns one Wave of Pillagers, and then, no more Pillagers gets spawned. 

It's also happening for the Pillager Patrols. 

Video of proof. 

https://media.discordapp.net/attachments/332971439554691077/1185014941284048906/SVID_20231214_181744_1.mp4?ex=658e122a&is=657b9d2a&hm=613854157149b85761ab7842dd330aaa693251fedbb7f619573c304d9ea20ab0&