@Burgi I know why. Let's not kill another online publishing business.
Nobody understands why ads have gotten this way.
Traditional banners are worthless.
I would much rather have to pay upwards of $100 a month for all the sites I want to see (in addition to the usual Internet access fees) than to block all ads.
It's unethical at best, and illegal at worst. Some website terms of service state your consenting to ads is "consideration" for access to content. Blocking ads would therefore be grounds for a civil suit (breach of contract, failure of consideration), and possibly criminal prosecution (as you wouldn't have a valid license to the copyrighted content, even if it's free). (IANAL, but entirely plausible legal theories...)
Even if there wasn't a legal issue, it just doesn't sit right with me to block all ads everywhere.