There are some really shitty BGs.
I won't even name any, simply because I know most will agree on which are particularly terrible. Of these bad BGs, I argue >5% of players actually enjoy them, while the remainder of players absolutely resent them. Perhaps they tolerate them, through conditioning, but given the choice, they'd prefer a different BG. These BGs are often slow-paced and require a larger amount of players, in relation to other BGs. So, to cater to the ~5%, the game forces players to agree to play something that they don't want to play.
This sucks and all, but it shows the truth of a bigger problem.
Providing bonus rewards when queuing for random battlegrounds forces players to participate in something they may not enjoy. The current system of two blacklist options isn't enough to justify a bad player experience, especially when it's only in place to cater to a low population.
So, what do the ~95% of players do to combat these shit BGs? They either deal with them and move on, or they resort to botting so they don't have to deal with a bad experience.
Of course, the 'grinding aspect' of the game is largely what players bot. However, forcing players to participate in something they legitimately don't enjoy, is simply terrible game design. (you don't boot up Call of Duty, queue TDM, only to get placed in a fucking ground war)
TL;DR: forcing players to participate in BGs they dislike isn't the entire reason people bot, but is one of the incentives.