I'll give you an analogy:

Microsoft were the biggest tech company for a while because they were the first to introduce the PC.

Bitcoin is the first cryptocurrency so everyone jumps on board.

But then Apple came along and innovated its way to a higher market cap than Microsoft.

Some alt currency will come along, and people will want to jump in early to catch the rise up and you'd just end up with heaps of different alt cryptocurrencies popping up everyday all driven by the desire of their creators to essentially make money out of thin air.