but what I'm surprised is that all the popular Altcoins in the market have not reached their new ATH after having reached it together with Bitcoin in the previous 6 months.
You wouldn't be so surprised if you looked at altcoin prices against bitcoin instead of against USD. You can clearly see that not even a single altcoin has been capable of reaching 10% of the ATH they used to have back in 2017 (the super altcoin pump year). The only reason their USD price shows a rise is because bitcoin price has been going up otherwise they have been dumping hard over the past 4 years which is clearly visible in their price against BTC.