Investors understand that Bitcoin is the most popular cryptocurrency and most investors invest in Bitcoin and that is why Bitcoin has gone so far from other cryptocurrencies, but altcoins are also very popular and in demand and may be much more popular than Bitcoin in the future.
Altcoins more popular than Bitcoin? I don't think it will ever happen.
The only way in which Bitcoin could lose its dominance is if it died or had a critical flaw. If it happened the whole market would take a huge dive and possibly all cryptocurrencies would be abandoned as investors become discouraged.
You'd need a dark swan event for altcoins to take over.