What I am wondering though: Do those groups just like being weird or do they actually hope to come out big?
Speaking of 'the dark side'; this
article about Necronomidol provides some interesting insights about your question (and more).
How is that even the same group, LOL!
It seems that idolgroups that don't have a regular, permanent producer are just all over the place concerning their musical direction.
The good thing imo is that things can get remarkably experimental for an in essence commercial product.
But the flipside is that groups like YRMRM! don't develop a unique sound of their own but just sound like the band who wrote the song. They just sound like Polysics on one their singles ('Hamidasumo', which is a really fun song by the way) and completely different on their next/previous songs, like you already said.
It must be hard if you're a fan of these kind of groups, you never know what to expect next. I guess they expect people to become a fan because of their image/looks so they can get away with any musical change, how radical it may be? I don't think this stands in the long run.