Blockchains need to be money to secure themselves economically. All monies compete. In the long run, the one money with the best monetary properties wins. The rest are shit. Ergo, shitcoins.
Discussion
That would only be true if the sole reason for the existence of every chain in the world was to have a coin. Once you introduce differing functions then the coins become coupled with the chain's underlying function, and therefore different from each other in kind, making common-denominator value comparisons somewhat absurd, like saying t-shirts will win out over socks in the end. As long as people need socks for their feet then sock coins will be valuable in a value-context all their own.