You're not wrong, but please note that those are Trump loyalists that followed him to a service that Trump didn't actually use until quite recently:
https://www.pcmag.com/news/trump-makes-first-post-on-truth-s...
It kind of seems that far from being ignored, network effects were the main reason Trump was using Twitter in the first place.
If you dislike Trump but want to monitor his actions, following him on Twitter might make sense. Joining a platform dominated by Trump supporters probably wouldn't.
These days YouTube does nothing to promote posters that aren't rich and/or famous already.
Having my own site and embedding my YT content is the only thing that helps me to be visible amongst a sea of celebrities who are already popular and promoted for free on the front pages of social sites like Twitter and YouTube.