Every app wants to capture all of your time, but what these app companies don't realize is that it's sometimes better to do one thing really well and capture 100% of time spent on that particular thing.
TikTok already handles text posts - it's called "teenagers pointing at captions on their videos and making faces". It's the culture, and TikTok has excelled at this very video-focused culture. Adding text posts will bore the sorts of people who are on TikTok for videos and may result in less engagement, not more.