Many people moan because many people have lost an incredible amount. Imagine buying Bitcoin at 18k and then lose over half of it? You would also spend a lot of mental energy thinking about the future and when it's going to go up.
They were unfortunate enough to have gotten swept up in all the hype although there were plenty who bought at the last bubble in 2014 but held through the downtrend and ended up benefiting from this one
Smart money comes in when the price is near the bottom not whilst the market is over inflated