If the projects shown would use a dowel jig, you would only get one video per month from your favorite channel instead of one per week. Additionally, it would be extremely uninteresting to watch the YouTuber use the dowel jig after the first 2 videos you watch because it is tedious and not very interesting.

And I really dont see the point. As a hobby woodworker you would be able to complete the projects with the same result by using a dowel jig, it would just be more work for you. When they say "I use the Domino because I have it on hand, but you can use any tool that you own to join these boards" that really is true. The Domino does not change the outcome, it just makes the process easier.