On the Polymarket homepage right now, one of the featured markets is whether or not Bitcoin will be up or down over the next 5 minutes. It's hard to justify that as anything more than illegal gambling.
I find prediction markets to be interesting on two fronts:
1) They like a really good way to determine the probability of something happening, which is interesting for events like elections
2) It provides an avenue for smart bettors to take advantage and sharpen their skill, whereas they get severely limited or banned from traditional sports books
However, it seems like all incentive structures for the markets and consumer behavior will steer these things to degenerate gambling.