A few years back, YouTube made Autoplay default. Human behaviour makes it much harder to opt-out of something that is auto-opt-in. Even turning a little switch is cumbersome and requires some mental effort to go against a system. However, it’s probably the best for all of humanity if autoplay were disabled by default.
First, watching videos without aim isn’t the best use of time, even if one wants to relax or is tired (especially the latter). It’s probably a good idea to know what you want to watch going into a watching session.
Second, we are highly influenceable by what we watch and may be exposed slowly to more radicalized content to keep us engaged with videos (and keep eyeballs on ads). I don’t think watching on autoplay leads us to being better people.