Because Bitcoin has the name and was growing fastest. The others were insignificant and likely to be fizzle out. But now they are starting to affect the price of Bitcoin. It is this increasing competition that brings into play the paradox making all crypto curriencies an unsafe investment driving people to pull their wealth out. Their growth is a threat to their growth.
We are already seeing what? Bitcoin didn't drop from 90% of the total market value until POS and ETH arrived, which are innovations, not clones.
I'll believe your paradox is valid when I see it--my hunch is that Bitcoin will be replaced atop the leaderboard by disruptive innovation.