Because they only want you to view the videos that make them the most money. They are in the business of selling advertising not the entertainment business
I started watching a channel, when they don't post new videos I start watching it from the beginning as I didn't find it until a few years after it started
Because when google takes something over they monetize it, stick ads all through it, record every click you make and push ads related to your emails or anything else at you, don't really care about the user because they are the users. Some corporate genius makes decisions that screw it up. And if you try to control your ads or don't take up paid options they push ridiculous semi-fake ear wax ads or similar.
senseless changes, like with all the updates they make to the format, i think those in charge are trying to annoy the original youtube users and succeeding at it.