Why is Ranked matchmaking done by "MMR" and not your current rank?

The system was designed using MMR originally and still uses the same concept - Honestly, tiers were just thrown in there to make people feel better about progress and not just staring at a number.

I remember back in Season 3 I think, all I could do was stare at 1450 on my page. It didn't really feel like I was progressing and just trying to keep my number high.

It's a lot easier to climb now early on then it was before. You got remakes now while before it was just an auto loss, when you're at 0 LP you won't fall right away, and you get free wins in promotions. I think it's a better system for climbing.

Not to mention just because your ranked something, doesn't mean you should be there. MMR helps drop or rise players who are not performing around the average person in their tier.

Because your MMR is your true ranking statistic. What we see - divisions and tiers - is just some gimmicky stuff Riot came up with to hide your true score, since players felt bad about seeing a “score” instead of a “rank”.

I would think that adding a strict divisional component would lead to a large increase in queue times.

Smurfs will ruin the game, if people get locked in "division based matchmaking". Maybe you don't u haven't seen it, but smurfs generally play vs other smurfs now, because they have way higher MMR, despite being in the same division as you.