Why is Riven Viable?

I saw a thread, Idk where it went, where it was complaining about Riven. And any nerfs that people came up with, there was a counter argument as to what buffs she would receive and how it would just put her back where she was prior to said nerfs. Now what I'm wondering is, why does it matter? Why not give her the nerfs, not buff her, and let her just.. kinda.. be mediocre? I don't understand the need for Riven to be strong. Not a lot of people ACTUALLY main her. I would say most of the people I see play Riven are really, really bad at her but she face rolls so hard, it doesn't even really matter. She has high potential in terms of mechanics and I respect a good riven when I see one, but when she 100-0's the ADC by closing her eyes and throwing her keyboard into the sun, it's a bit much. I mean.. Olaf was never fixed to be super viable. I don't get it?

Riven is like a mosquito. No real benefits except for the death of a population.