You have to understand that due to low player activity, there are situations where battleground groups have either fewer or more healers. Moreover, if such a system were implemented, one battleground would have a full 10v10 match, while another might be empty or not start at all. As a result, some players who queue as healers could end up waiting for hours for a battleground to pop.
On top of that, put yourself in the healer’s shoes - you're the only one trying to keep the whole group alive, while two Affliction Warlocks focus you, making it impossible to heal no matter what you do. Even if you take a Shaman, the strongest AoE healer, they would still be completely useless in that situation.
It's not just about Affliction Warlocks - if there's only one healer on a battleground, they won’t be able to do much against nine competent, skilled damage dealers. Healers would simply be out of the game, and classes like Holy Priest and Holy Paladin would be useless in battlegrounds due to their weaker healing compared to other classes.
You just don’t play healers and don’t understand how difficult, and sometimes even impossible, it is for a solo healer to keep the entire group alive when facing strong damage dealers, especially those with decent AoE healing.
The person who understands the situation best.