BCH retained value because it represented a large portion of the community, and the goal was a soft fork rather than a hard fork so quite a few people participated in the switch.

That kind of thing will happen less and less each time a large, informed group of people leave BTC, till all you are left with is a fool's market.

It also helped that the portion of the community BCH represented included the owner of bitcoin.com and a few of the other major sites and services. (Also one of the major mining hardware providers, though I'm not sure how well that worked out - they forced miners to use it for hardware purchases at a time when it was borderline-unusable, which can't have left a good impression.)