Because businesses conform to customer wants/needs, not vice-versa.
Business: "No. It's $2. Please pay for the burger"
Customer: "Why aren't you conforming to my needs?!"
On top of that, I own my computer. I am responsible for the data which is transferred to my computer. I should have a fully-accessible offline copy of any and all data which is transferred to my computer, and not one bit of data should ever be transferred from my computer without my express consent.
Adblocking comes to be a multifaceted statement. It is anticorporatism, it is privacy advocacy, and it is a declaration of data ownership & responsibility. And for some people, it's accessibility layered on top of one or more of those.