"came out of nowhere"? that doesn't mean anything in crypto. bitcoin isn't even a decade old yet---every significant business comes of nowhere. binance looked like an ICO scam 1.5 years ago. kucoin has barely been around for a year. neither were considered trustworthy until fairly recently.
the reason upbit got hyped so much is because they partnered with bittrex (to share order books etc) when bittrex was the biggest altcoin exchange in the world. in mid 2017, bittrex was a very big deal.
i'm surprised that you're surprised. this market is perpetually rife with greedy noobs looking to get rich quick---what do you expect to happen?