Aren't most advertisements served by Linux servers these days? Free software isn't a monastery, as utopian as that ideal sounds.

the OS of an ad platform is totally not important. I fail to see how this is relevant at all.

I’m not sure which user we’re talking about, but it’s up to the video.js user to decide if and when they use ads. Just like it’s up to YouTube. Video can get expensive, so some video wouldn’t exist without some form of monetization.

The user who uses the software running in his browser.

The user can still ad-block. Or choose to let the ad to run to fund the video producer.

In this case, you're talking about the browser user, and not the dev user of video.js, but I feel like you know this and are just trying to rail against ads in a manner that's just not relevant.

If someone providing video content wants to run ads as part of making the video available to you, that's up to them. It's also up to you if you want to attempt to view the video without those ads or skip watching altogether. But to the dev of video.js, you're personal choices of consuming AVOD content are irrelevant.