Yeah, you hit it exactly man.
The most common vlogs seem to be young 20something bro-science dudes who have the time and skill set, and desire, to do it. They're also not talking much about the science, the methods, the mental approach to the prep, etc., it's all "watch me workout", "look at the macros of this sandwich I'm eating," etc. I did try Instagram for about a month and change, and honestly I just couldn't get into it. I was hoping it might get some clients, and I quickly realized in order to potentially see ANY ROI at all, it would take way more time than it'd be worth. I've gained a lot of clients locally over the past few months just from the gym and word of mouth, good enough for me. Instagram and YouTube don't need another guy talking about training and macros and coaching.
If I'm going to spend that much time doing something, I definitely need to make some money. I have a mortgage, a wife, 2 dogs, a business, and as @IronAndMetal pointed out, a lack of calories, sleep and general motivation during a prep. I don't have hours a day to spend recording videos and editing and all that. On IG, IMO, the people that get thousands of followers seem to be some of the most vain people I've ever seen, no one cares about the science or the methods, they just want to see ripped people showing as much skin as possible and see how many followers they can collect and how many "likes" they can get. I'm not doing this to collect followers. I am not criticizing anyone reading this who might be into it, to each their own for sure. Just not for me.
I like keeping a log on T-Nation, compared to other sites, or a vlog, because I believe the people that come here and will read my log here are genuinely interested in the process, in the sport, and hopefully it can provide some knowledge and motivation along the way, as other prep logs have done for me. The thought of putting something on YouTube for the whole world to see, criticize, pick apart, I'm just not into it.