It is both greed and fear combined for both buyers and sellers. Sellers FOMO on further price gains, buyers FOMO due to the same and thinking they will be forever priced out. Buyers greedy to think they will make quick money out of still rising prices, and sellers greedy to take all the gains up front so the buyer is left with less chance of significant gains. Both sides of the same coin.
I often see it with homes in my area. It goes on the market for 2m a month later it’s 2.5m usually it gradually drops to 1.5 in 100k chunks with in a year until it’s either sold or pulled off the market. It’s almost like people read articles about crazy market and willing to sell only if they get x for it otherwise they don’t really have the need to sell.