the way the newer instagram algorithms work, the average time spent by a given user stuck on a post (watching the video, reading the captions, comments...) determines how important of a place the next posts by the same uploader will take on their news feed (at the expense of their other subscriptions they more rarely check). that came around the time the super slow-mo mode came out on iPhones. I'm guessing that dictated a sudden need for drawn-out content in advertising, which in turn impacted skateboarding and then of course, everybody started doing it and it became a trend. now people use it to try and make even really ugly tricks look cool. but the novelty aspect is wearing off, but business-wise the original point still stands and more than ever now that most everybody's got something to try and sell, and has access to such modern, accessible branding tools.
I like the skating I watch super quick with no dull moment à la Traffic, so in general and not just on Instagram I'm not a big fan of slow-mo. I'll only occasionally slow-mo tricks that have something particularly weird going on and even those I tend to prefer seeing in real speed, raw.