I don't watch twitch so I couldn't say for sure, but maybe the ads use the same servers as the stream so ad blockers are unable to distinguish it from the real content.

The ads are the most important part. Just relax and enjoy the ads. They will make you a better person.

Because they deliver the ads on the same data stream as the actual stream you're watching. Last I checked there are ways to get around it, but you have to go through a lot of trouble, can only watch in 360p and the actual stream is still delayed by 30 seconds. It just shows some bullshit "there may be an issue with your browser" message until the time that the ad would have been over. Haven't checked if these methods still work though.

I just use BTTV to start all streams muted and switch tabs immediately after visiting a streamers page. Blocking the ads really isn't worth the trouble.

Mute works great