Isn't it common knowledge that many sites rely on ads for their revenue? Sit-down restaurants in the U.S. don't tell you as you walk in that you're expected to tip, but it's common knowledge that wait staff aren't paid minimum wage because customers are expected to tip. Yet, it's generally considered rude to not tip even though it's even easier than installing an ad blocker and restaurants won't refuse you service, whereas some websites try to block ad blockers.
Edit: Added last sentence.