TikTok isn't about movies, it's about short videos pulling in your attention. They aim for the mobile phone.

Also if a video is showing a single person (standup comedy?) vertical can show them closer, as people (mostly) are vertical.

But yes, for a full movie, where you have horizontal camera movement, a vertical screen gives too little orientation for following the movement.

In painting and photography horizontal and vertical coexist for millenia. Based on the motive and purpose.

So noted, but I suppose you'll define which movies are great and which ones don't count? TikTok's popularity demonstrates a demand for vertical video, despite how much you don't want there to be, simply because that's how people are viewing video - on their smartphone. Even Netflix is doing vertical video clips for previews. My prediction is we'll see a mainstream movies be recut/reframed to be vertical on Netflix/other online streaming service simply to complete with TikTok's content farms.

Don't watch movies on tiktok then, lol