I think why other alcoins can't replace bitcoin because bitcoin is the king of other alcoins no one can replace the king. alcoin was born because of the creation of bitcoin if bitcoin was not created by satoshi nakamoto maybe alcoin did not exist until now,
everyone is aware that bitcoin is general overseas of cryptocurrencies. But some of us don't know that altcoins make bitcoin relevant and also bring many investors to market, because bitcoin is already existing before other discoveries of altcoins. For me i may not like to invest in bitcoins again because the profit can not use to compare to the profit new coins will give me if i invest, to summarize it all. Every one values altcoins instead of bitcoin and if you watch carefully you will see that many of the altcoins is having same credit of bitcoin
indeed the most important thing is because bitcoin is the oldest coin, therefore it seems that it has got a brand, so that in its development it has gained great trust from investors. and that trust is what makes investors seem to unite their thoughts to invest in bitcoin, so that other altcoins seem to follow the movement of bitcoin because of the influence of the thoughts of each investor.