Can someone explain why rivens passive doesnt work on towers

So im a bit confused as how the towers seem to work these days and was wondering if someone could explain to me why passive doesnt work on the tower? The passive just adds extra damage to her auto attacks. Which one of the reasons why she hits so hard with her auto attacks. "Riven's abilities charge her blade, and her basic attacks expend charges to deal an additional damage." that is the exact passive from in game. No where on there does it say only against enemy champions. It works on everything but towers and the nexus which i don't understand when you have things like q working on towers or q which he gets to stack and lets not forget if they build tri-force they also get that. Even was updated to the point that her q works (minor) and her e lets her crit on the tower. So can someone explain to me the purpose of this? I know a lot of people just hate Riven because she is this play maker so i ask if you can please keep that yourself cause I am genuinely interested in the reason behind this. It would help a lot with her ability to take towers and based off the wording passive it sounds like it should apply.

Note i do not play ranked as i have no interest in that. It seems way to toxic for me so i play normals just for fun but i tend to face on average gold players however ive also been playing with a diamond friend so maybe plat in our games. The point is i do understand the game to an extent and watch a lot of league players who explain how the game works and so on.

I have just never heard anyone explain why this is and if it should work it would be cool to have riot update that or at least answer why for me if no one else can.

For anyone who reads this and takes the time to answer thanks and good luck on the rift summoners!!! [slayer-jinx-catface]