Of course everyone makes his own personal choice. That doesn't mean that there are multiple human wills. In fact we never say 'human wills". It sounds strange in English for valid reasons that cannot be dismissed.In Spanish and English we sometimes use that expression metaphorically, in the same way we say "human condition", "human progress", "human destiny", etc.
But obviously, each person enjoys or suffers his own condition, is accountable for his own progress and will face his own destiny.
In the case of will, the fact that there is no single human will is clearly manifested in that every person can make his own choice and will be judged and rewarded by God according to his own deeds.
We believe in individual salvation, don't we? Well, Individual salvation is based on the concept of one person = one will.
In conclusion, the entire human race is not one person precisely because it is composed by billions of wills. One person = one will.