because until now, only bitcoin that could help us to make money, I mean help us to convert our btc into fiat and I think every seller is accepting btc than other coins. beside that, bitcoin is more famous than the other so people prefer to choose bitcoin. if we visit into localbitcoin or other exchanges that allow us to send the fiat, localbitcoin and other exchanges giving an easy way to us to exchange our bitcoin to fiat so bitcoin is better than any other of these crypto currency.