MMR Displayed?

I know league revolves around mmr and how you are doing in game, but why is it that you can never really see how you do comparably to others on client or on the league of legends site? There are sights like op.gg that show you an estimated mmr and how you are doing, which shows if you are climbing in mmr or if you are slowly dropping. It's not always 100% accurate as its a brief estimate, but why hasn't riot made an official mmr that we can see? Within client or even on their main site? I know you have your rank, and that's based off your mmr and placing. I know there is sites that show your mmr, but why doesn't riot? Bad idea to show people their mmr in client or is it just better to have your rank be your based mmr. Only reason I think this is during preseason you just get about 1 elo below yours, S1 to B1 it seems as example. but your placements are off mmr and you really cant tell that.