Majority of those coins on top 20 are old coins and few are new ones with different network or chain. This year is the surge of defi's and nft's the new trend that is why new coins comes from these kind of projects. Bnb made it to the top 4 and also polkadot has shown good performance at top 6.
I am not following the market for sometime and if i look at the top coins in the market i am seeing new coins and the old coins are replaced by them and this is not surprising but i am surprised to see many new coins in the top list. I never expected BNB to be in the list when there are much better coin in the market and yet they were able to be in the top list.
