Why do Luke Smith and Mental Outlaw have youtube channels? Why are some of RMS' talks available on youtube? I'm not comparing myself to those people who definitely have a much bigger platform than me, but the philosophy is the same. In order to reach the widest audience, you must use a wide platform.
I could use Mastadon or lemmy to post about my opinions of free software, but that wouldn't be effective. Why? Because most people on those sites agree with the free software foundation or at least with the idea of free software, it would be preaching to the chior.
I chose instagram as it has far more users than mastadon and lemmy combined. During my time on instagram, I have influenced people to at least try linux, some went back to windows, but most liked what they saw, and still use it as of writing this. Sometimes, to bring free software to the widest people, you must use a proprietary application. That's my philosophy, and I will stick to it for the near future.