It's without question aimed at and useful primarily for a young demographic with an extremely short attention span. It's also really hard to create long-form quality content, the short clips remove that pressure, which is exactly what short tweets accomplish (the typical TikTok user is creating absolutely nothing original, they're all directly copying eachother; you have a tiny number of originators, and then everyone else is a clone (a mimic), which is humanity in a nutshell). It's mostly about status battling, young people fighting for some attention, trying to put a stake in the ground to claim status among peers to position themselves. It's why so many of the most popular users live in nice locations, in mansions or otherwise huge very nice homes, they're envied, they're pitching/riding status to a million followers. The sex selling, faux-dance cloning and ass shaking (WAP WAP WAP) that the majority of of the non-celebrity popular users use it for, tells you everything you need to know. It's the same thing that made Snapchat popular, sex always sells. TikTok of course derived from Musical.ly and was popularized first in the US among teenagers. The content that fills up the platform is still similar to what originally made Musical.ly popular.
TikTok is the Kardashian effect brought down to the masses of people, to roll around in. Mimic in just the right way and you too can be Kim for 15 minutes (if your house is big enough and or you're attractive enough, as you have to be able to sell it). TikTok's most popular non-celebrities are pitching exactly the same thing that made the Kardashians so popular, in the exact same way. It's a cultural wasteland, celebrated.
What the hell is anybody going to say in 10-15 seconds that is going to be valuable outside of a quick clip of music and some status pitching (show a big house, shake your ass, take off your shirt, dive into a pool, show seven seconds of a party)? Absolutely nothing. It's the same thing Instagram is mostly used for: status positioning, signaling. There is a reason why the evidence overwhelmingly points to all of this as being unhealthy - it's all built around intentionally amplifying an addictive, desperate aspect of human nature that is a big negative at its extremes (status seeking, narcissism, bullying, social competition, selling sex, all in a swirl together and pumped up).