Dom Hofmann, one of the cofounders of Vine launched Byte which is basically a new Vine: https://en.wikipedia.org/wiki/Byte_(app). I don't know if it's catching on though. I guess if TikTok does get banned we'll see a mass migration somewhere.
Vine launched in 2012. There probably wasn't a critical mass of mobile phone owners, specifically teens, at that time. The iPhone hit the market only five years earlier.
It's difficult to understand why Microsoft wouldn't buy this. With some clever marketing I'm sure they could grow the username rapidly and it would cost less than 1% of whatever TikTok would cost.