Why are altcoin exchanged for btc and not for dollar?
having tons of altcoin is just like having bitcoin. If bitcoin grows, they grow. If bitcoin falls, they fall.
Isn't this pointless? Why not buying and selling alts for dollar?
Because traders always want to take advantagenthe volatility of bitcoin, yes it may decrease in value but traders are confident that it will increase more than it decrease and by holding bitcoin it will grow a significant amount. And if we're just sticking in fiat we can't experience how crypto currency really work.