The fact that people only ever get autofilled to bot says a lot.

I don't know if there are any hard numbers for what roles get autofilled the most, but I'm ready to assume that ADC is #2 behind Support, because ADC is the only role besides Support that I have ever heard of anyone getting autofilled to. Support being the most autofilled role makes sense. People come to this game with the mindset that this is a multiplayer action game, and support is the role which fundamentally is the least effective at interacting with enemies by itself. Therefore, most people won't want to play support. But ADC is quite literally the opposite. Its the role which is typically the best at impacting the game through damage. So the fact that its relatively common to get autofilled to ADC says quite a lot about the general playerbase's dissatisfaction with the current dynamics of playing botlane.

So what reasons, besides the ones inherent to the lane, do people have for not wanting to play ADC and Support? I would guess, based on my own experiences, that its not a problem of the champions being unsatisfying to play as, but rather being abysmal to play against. The inherent lack of counterplay to an ADC's damage pattern makes wins feel unearned and loses feel bullshit. But beyond just ADCs in general, bot lane is home to a number of the most frustrating and least interactive champions in the game, and even worse, most of them are comparatively strong. Sona, Janna, and Soraka are the big historical offenders, though that's not to say tank or mage supports can't be a problem in this regard (cough cough Leona Zyra cough).

If you have any other ideas as to what makes these roles, ADC in particular, so unpopular, feel free to post.