Because DEX trades tokens on the bitshares blockchain. People like to buy the blockchains actual token. There is a huge difference.
Liquidity is
a the major problem,
after that it is still hard to tell if BTS is not pure BS ... it was build upon a mountains of lies or fraudulent misdirection ... but the Aces in the hole are a nice working demo, all the other vaporwares do not have this.
So old school blockchains 1.0 actual coins on chains that the average G.I. joe can download are more accessible and less risky than a BS token.