TV is a closer analogy, but back in the days of broadcast TV, you had to get airtime with one of a dozen networks. (And Trump did this! He had the number 1 show on TV for awhile in the early 2000's. He continued building his brand as a "rich guy who makes deals" there.)
You can't just come back the next day and broadcast another message, i.e. testing what works and iterating. It takes a whole team of people to make a broadcast. Also, the audience would watch TV at home; they didn't have a device to consume the message anywhere. It was fundamentally slower.
Even blogs are slower, although you can definitely get deplatformed for a blog. Blogs lack discoverability; they don't broadcast to followers. In the heyday of blogs most people weren't reading them on their phone.
So social media, and Twitter in particular, is a really effective communication technology for broadcasting sharp messages.
Telephones do have similar issues -- there is a reason that wiretaps exist and that traditionally the phone company was a monopoly with close ties to the government. But they're not a "platform" for broadcast.
FWIW this isn't really adding something to the conversation, not that I've been paying very close attention.
I believe Facebook and Twitter already had a "heads of state" clause in their policy that recognizes this.
Yup: https://www.theverge.com/2021/6/3/22474738/facebook-ending-p...
In other words, heads of state were already allowed to say things that normal users aren't, based on the reasoning you state.
According to executives that made a one-off decision, Trump crossed those more relaxed lines.
Of course a lot of it had to do with the transfer of power in the US -- he would soon no longer be a sitting president.
As Yishan says, these decisions aren't really based on "principles". They are based on "shitstorms that are brewing and that we want to avoid", of which January 6 was a perfect example.