Riot and slows

I was just wondering what riots stance on slows are. I mean we have riot coming out removing silences from assassins and possibly more. Yet they add a slow into tons of champion kits which essentially is a nerf to bruisers and tanks, more specifically tanks and bruisers with no gap closers.

As a side note I also would like to know, why Riot slaps slows onto knock ups and other CC type abilities. For example it doesnt make sense that stuns (which can be reduced by tenacity) dont get slows yet knock ups, which by the way cant be reduced by tenacity, get them slapped on all the time. Just seems very counter intuitive to me. (There are 1 or 2 exceptions to this rule) Taking a look back in time when Janna originally came out her ultimate not only healed and pushed enemies away during the initial blast, but any enemy to re-enter the healing zone would be slowed. Yet Riot removed the slow because of just how much of a difference it makes. Yes I understand there has to be differences between champions or else they just become cookie cutter shapes with different colors on them but i dunno, the amount of slows on champions now is seeming to fall under that category none the less.