When I didn’t fly all the time, I didn’t care about loyalty. But I did 160,000 actual airline miles (far more FF miles earned) last year (most of them on one alliance, but enough to get lowest tier status on two others) last year and at this point, I’ll pay extra for Delta because I get auto-upgraded to Comfort+ at booking, I have a very good baggage allowance regardless of service class (assuming I’m main cabin and not basic economy, which I wouldn’t do anyway), I have a lounge membership, and I get frequent upgrades. At that point, my comfort and those benefits are way more important than saving a few dollars across airlines.
And that’s the problem with these types of services, I think. They cater to the occasional traveler who doesn’t travel enough to make a profit (unless you’re Google and you own the software everyone else has to license), whereas the frequent travelers are either booking through corporate tools or directly with one airline because they have loyalty — or both.
Catering to then majority of flyers who fly once a year, when margins are what they are on flights, is a tough business. It is interesting that Hipmunk's parent company got a piece of my $60k in travel last year (most of that was work, maybe $2500 was personal), because that’s where your percentages can matter.