The problem isn't so much blocking the ads on a page, that's a solved problem, it's doing so without incurring side effects. The main problem usually comes in two ways.

1. Ads are now being pre-baked into the content delivery itself in which there is no easy way to rip it out without destroying the content in some way. Twitch is notorious for this on streams where the ad portion completely replaces the video feed before your browser ever sees what was originally there. You may never recover what was there, but if you try to block the ad playing you trigger problem 2.

2. There are departments dedicated to developing ever changing anti-adblock scripts and detectors that enforce ad placements and detect tampering. In some cases this results in punishing the user by refusing to deliver content until the ads load, blocking or kicking the user off the page, throttling connections or access, or in Twitch's egregious case, more invasive ad interruptions. This has become a never ending arms race with ad blockers to keep up with minefield of invasive scrips monitoring what you do with their website.

TLDR: Ad blockers like UBlock Origin are already filtering how you're asking for bur advertisers are attacking the plugins themselves and have their own arms race of scripts to punish those who interfere.