As someone who's dabbled in flights bookings (BookWithMatrix) and now am working on a travel startup (Wanderlog, https://wanderlog.com, a Google Docs/Trips for travel planning), flights are just not that profitable. In North America, you'd be lucky to get 1-2% commissions. In the rest of the world, it's a bit better, but Hipmunk was definitely North America-first.
Concur never was a consumer company and Hipmunk never was going to make a ton for them, so it was just a matter of time. RIP -- a lot of their best features (not just showing the cheapest flights, but the "Best" based on agony) have made it into all major meta-search tools, so it's not for nothing!
(Also, I personally use a combination of ITA Matrix, Google Flights, and Skyscanner now. ITA Matrix still has time bars, if you loved that UI; Google Flights is just so fast, and Skyscanner searches low-cost carriers that Google Flights sometimes misses)