According to an interview done to the producer of the anime, there were several reasons:
The animation originally was meant to be broadcasted in web format only, not as a TV series. Then the author asked the producer if it was possible to record two tracks: one with female voice actors and one with males and broadcast the primary track and the auxiliary. ...
I'm not entirely sure as to why they've repeated this in further episodes, however it might be due to contact obligations with the voice actors needing them to have a full length run of work or not at all, perhaps cost-wise it was also more effective, etc.
However, the reason they have Male VAs in the first place is due to a gag within the manga where they ...
Here (1, 2) are the YouTube videos by 333ユグ playing the scenes for Part A in reversed.
Here are the reversed conversations for both Part A & B (source: Mr_BlueSky's Hatena Blog (Japanese)):
When passing the window:
"Co, cold, cold..."
(Because Blackboard Goro is too noisy, it's impossible to be ...
I have a couple of answers, unfortunately they're all a bit speculative because I have no sources.
It feeds into the main premise of the show, which is surrealist humour. It's not meant to make any kind of sense, and it has a slightly unnerving result because it triggers a deja vu in the watcher.
It lets them try different approaches to the same premise. In ...