Pillagers don't spawn around their Outpost with the floating island generation in 1.14 Pre_5. The difficulty doesn't change that.
For reproduce this bug, just create a world with floating island generation in buffet and a biome with outpost (plain, desert, taiga, savanna and tundra), and a /locate.
And just see the no presence of pillager...
This may relate to MC-147360, but it has a different cause since pillagers are strictly coded to spawn over Y:63 instead of the set sea level.