The big coins will keep being top coin because they got the concept of blockchain earlier. It's not easy to beat the original idea to the top. People get used to the first things they use especially if it provides them all they need. Bitcoin provides its users with excellent services likewise some of the earlier altcoins. Most of the new coins are just trying to rebrand what we have already and they fail, mostly because they lack ingenuity.
It seems to me that most of the coins that enter the market do not come out. Just collect money for your ideas, projects, etc. and ultimately just invest their money, investments in bitcoin, ether .... Therefore, they are not able to surpass the top coins