Miss Fortune Nerf Question

I don't mean to sound petulant, whiny, uninitiated, or unaware when I ask this.

Why is MF getting a nerf at all?

The reason I ask this is for several reasons.

My understanding is, that before Season 6, she was considered trash, and saw very little play. During season 6, she floated in and out of mainstream use, but never truly fell back to her previous levels of disuse.

Now, in Season 7, she's been an oppressive force sure, but according to stats available to me, she's at no point been, the most played, picked, or has had the highest win-rate. She has been what I would consider to be strongly dependable.

Now, some people see this as a buff, most see a nerf, and it can't be argued that the base numbers are being tuned down, but the extra damage is being also turned into Critical Strike based damage.

I would posit that also changing the bonus damage into critical damage is an attempt to enforce a crit-based build on her, like so many say. However, this adds an extremely unpredictable element that this could force her back into a minimally used state. (Again my understanding of the true ramifications may be poor.)

Riot seems to want a more diverse representation of champions to be used, then why are we not seeing Varus or Jhin being affected in such a drastic manner? (Jhin saw a very gentle nudge recently, but continues to see increased pick rate.)

I'm not looking for numbers, or short-hand comments to the effect of "she's oppressive!" She can be a lane-bully this is true, not all the time, but in the right hands she can be.

What I am looking for is help to why this change is occurring at all, like the reasons behind it. (Especially when it seems that her pick rate & win rate seem to be on the decline anyway.) It feels very left field to me.

Please don't comment telling me I'm trash or some sort for not understanding. That's why I'm asking, I want to understand better.

Edit: Teemo is the absolute worst. (I didn't finish reading the forum guidelines.)