How does the ranking system work? Why use LP?

Hello fellow players -

I just had a discussion with a friend over how the ranking system in League works, and being someone that really likes to know how things work, I'm really puzzled with the ranking system.

(These boards don't look very civil and educational, so I'm not sure this is the best place to put this)

I know there's MMR and LP, and I know that there's a lot of "rules" or ways that they interact with each other and determine your placement or who you are matched with. I don't really want to list them all out (and there should be a page that does...(I couldn't find one, it was hard to search these boards)). But to me, it seems like your MMR dictates how easy/hard it is to gain LP, and LP is kindof used to rank you.

My question is - why not just use MMR to determine your rank? And why keep it secret now? Can someone thoroughly explain how the system works, and why they chose to do it this way? I know that's a lot of work, and no-one will probably do it (or even knows), but it's worth a try. The whole system seems really confusing and unintuitive, and I see that people get really pissed off at it because they don't understand it.

Maybe even Riot could see this and join the discussion, but hell, that's gonna happen :/

Thanks everyone

• Spemble