Don't know why people buy anything but BTC.

More like why would anyone buy a relatively new altcoin when the market is in the bear mode and every time BTC drops its price, that altcoin is more likely to drop further. Worse, that new one doesn't have a strong support base yet (new, remember?) so it is also more likely to get hit harder if fud/bad stuff happened to that altcoin which in this case, Optimism hacked.