Why do I watch Booktube? Why do I watch your videos? The answer to these two questions is quite simple, I like hearing people talk about books. Personally books are my primary interest in life besides my wife and family/grandchildren/the saints/the cosmos. I like watching people talk about books even if I do not have any interest (passion) for the kind of books they are reading. I enjoy watching videos in Booktube where the people come off real for example you, Steve, Paperback Junky etc. . . I agree with that observation you made about Booktube being like having pen pals. I try to make my own videos personal meaning I really want to be a bookworm friend/pen pal even if we read different kinds of books or have different world and life views/philosophies.
I watch videos in Booktube throughout the day. I do agree with you that I like to watch videos where the individual posts every day or a least once a week. Some of my favorite Booktubers have skipped town meaning they have stopped posting. I often wonder are these book lovers still living? What happened to them? Where is the love? My wife tells me people in Booktube do not have the time I have to makes videos so I should not be bothered if they have stopped making videos/life is for some folks more than making Booktube videos. Still I miss those Booktubers and hope they are doing OK.
Another reason I watch Booktube is discovery new writers/that is one of the reasons l like watching Steve's channel is when he shows the books he has gotten in the mail to possibly review. Well this has been a long reply to your question, but thought I would share some of my fleeting reflections. Keep making videos-peace