It does, if you use e.g uBlock Origin. Twitch is actively trying to circumvent adblockers but so far hasn't been able to topple the more advanced blockers, even though they released SureStream[1] almost 4 years ago which is supposed to "weave" the ad directly into the source stream.
In the announcement[2] they mentioned:
> We are well aware that many dedicated Twitch viewers use software that bypasses ads, and the rollout of this technology will reduce the efficacy of such software. As a company we are agnostic when it comes to the use of this software. You are free to use it, or not, as you see fit.
I suspect that either advertisers or streamers aren't using SureStream or that it's quite resource expensive to "weave" ads into the source stream so Twitch simply isn't using it when the cost of doing so is more than it generates in ad revenue.
