I have searched for the problem before write. Probably this bugs that one time was resolved, now is back in the version 1.14.1 . I have created one world in the version 1.12.0 and have build an pillager farm next to a outpost, and the pillagers captains at this time, spawns normaly, like 5 pillagers and one captain or something closely to this. aAter this i played a lot  until the games reaseches the acctualy version 1.14.1 , and the spawn rate of the captain pillager was the same when i started in the 1.12.0 version, and recently me and my friends decided to start a new world for us to play together from the start. After we create, the first thing that i decided to build was the pillager farm, and i built one the same way that i build in my old world, next to a outpost, and i have noticed that the captain pillager spawn rarely in the outpost. I passed 2 in game days waiting to the captain spawn and only normal pillagers have spawned in the outpost.

So i think that who created an world before the 1.14.1 have the captain spawn rate normal like i said before in my old world, but who created after the actually version are have the same problem. 

note: sorry for my bad english, im brazilian and tried hard to explain