Louie told an awesome story about why this season exists on Opie & Jim Norton's radio show on Wednesday.
Basically, he had planned to take another long amount of time off, like he did with last season. Then he got really high and wrote a whole bunch of material and called the head of FX at the last minute, literally right before he was going to announce that the new season of Louie was not going to be soon, so instead he announced that the new season was coming. However, since they already segmented money for other stuff because they thought the show was going to be delayed, he could only give Louie enough for 8 episodes.
The next day Louie realized everything he wrote was terrible because he was high and none of it was funny, so he had to start from scratch and write the 8 episode season he promised FX the night before.
Oh and he mentioned that another 8 episode season would be right around the corner, it'll be a very quick turn around for season 6