It's never just a matter of gains for the people who invest their money in top cryptocurrencies such as Bitcoin, ETH, SOL, and a few others. Still, it's also about financial security, and by financial security I mean the safety of the invested funds and them not getting wasted for which the odds are extremely tiny if you have it invested in the top cryptocurrencies. In contrast, if you do the same thing in new projects and cryptocurrencies, you will have a higher risk attached to it.
So even though it's true and known by everyone that they might get higher profits if they invest in other cryptocurrencies, they invest in the well-known coins for this particular reason and nothing else.