Beacuase it's an older coin widely accepted by many people over the world. But it may be changes as people start using other coins.Like Monero on dark web. Where BTC volume reduce and Monero volume increased.
Yes, I think of that too. Bitcoin is already been rooted deep in every investor's mind and heart. The trust snd reliability is with this coin. Though there are new potential ones and more are already using it, but still, I know the investor's top choice is still the bitcoin.