The comment you replied to seems to have a fair assesment of why it failed

>It's an interesting, and perhaps depressing case of a product design concept being far superior to what's available in the mainstream for a certain class of user, but cannot gain enough mainstream acceptance to be a viable business or even a well-supported service for those who love it. And far more than most other product categories, flight search has huge infrastructure costs, so it's very difficult to economically sustain niche products (from grim personal experience of being part of a team trying to build a novel flight search product ourselves).