It's not only a matter of being newer or superior to others that counts as far as long-term success is concerned. Please keep in mind the "standarization" aspect.
The popular qwerty keyboard setting is a good example. Most people are using it not because it's the best way to arrange keys on a keyboard, but because it's the worst one. A long time ago, when typewriting required strength and physical machines, the latter were likely to break if people were writing too fast. That's why the qwerty arrangement was introduced. It became popular and everyone was using it… And later on, when it was no longer necessary to use this arrangement, it was not possible to move to a different one, because… everyone was using it - nobody would want to buy a new keyboard and go through all the hassle with learning how to type once again only to write a little faster.
So, even if altcoins are slightly better, they might never be really better or become widely accepted because bitcoin has already become a kind of standard.