The ads is the reason why content creators post their videos on YouTube. The want to be, and deserve to be, compensated. His audience would shrink immediately if he were to self host his videos and his source of income would disappear overnight; leading to him doing something other than content creation to provide for his family.
For me, it's a little bit that, but probably just as much the bandwidth costs. I used to host some video content, but even if one video got 1/10th the views it gets on YouTube, it would be many TB of bandwidth, and that gets quite expensive.
The solution is to upload in like 360p low quality, but then any screen recordings are a muddy mess and there's no point.
