Since the emergence of Bitcoin, several alternative cryptocurrencies have appearted, although afaik none have them come even close to bitcoin in terms of popularity, trading volume and money involved.

Question: why? Is there something wrong with Bitcoin? What advantages do the alternatives offer? What does Bitcoin lack what the others don't?

It's my impression that these alternatives were only introduced by people who would like to be early adopters themselves, hoping to see their stack of virtual coins (which are cheap or free to obtain in the early stages) booming just like BTC. Or am I mistaken?