> why did Cloudflare never build an ad blocker despite many requests?

Many of us who use an ad blocker don't actually have a huge problem with ads. It's the tracking we object to.

I don't want Cloudflare to build an ad blocker, I want them to make a tracker blocker. Make surveillance so difficult and expensive and unreliable that companies stop doing it.

Unfortunately ads and tracking go hand in hand: without tracking, targeted ads are much less effective. If everything else stays the same, you'll just get more, bigger, and flashing ads to compensate for the inefficiency, like what you see today on smaller sites without sophisticated user data.