The real reason was there are some whales already taking profits but after Bitcoin dominance keeps falling the alts will fly and probably it is showing some signs as the major altcoin (Ethereum) is taking some leads and it backs up again at $1700. This isn't some financial advice but historically this has been done before way back 2017, I wouldn't be surprised if some alts will make some new ATH.
BNB surprised everyone with its recent rally because of the ETH transaction charges and people shifting their focus on the BSC platform and do you think you have the answer for the correction, investors will book the profit in ETH and will jump ship on BNB and so is the reason we saw a 20% correction in ETH. Already many alts reached their all time high this rally and hence it is not the best time to invest for any newbie in the market who have no idea what is going on.