Because the people 250 years ago could not have imagined the problems that we'd have invented for ourselves in these days. It was always meant to be a living document with a process of adding and changing amendments. And in between that time the the way people interact has grown more complex. If you took those same intelligent men and dropped them into today, the Amendments would look different.
It’s not a certain company, it’s a whole class of them (partially defined by POTUS’ whims)
Sure, the government can do that, and when doing so infringes on Americans’ speech or access to information, it introduces First Amendment questions that must be addressed.
“The government says CNN can’t post stories from BBC” isn’t immediately resolved by “it’s a foreign company.”
It sounds like you're saying that there's some content on TikTok that Instagram Reels/YouTube Shorts/etc. won't allow on their platforms. Is that correct? If so, can you give an example?