I don't think the Ridgeline is/was a poor seller because of its qualities as a "truck". I think the Ridgeline is/was a poor seller because it's marketed to a "sport/utility" type of audience but doesn't get "sport/utility" type economy.
You can draw an exact parallel with the Chevy Avalanche, also now gone. The Avalanche was every bit a "truck" as a Silverado 1500. In fact, they offered both 1500 and 2500 versions of the Avalance. But like the Ridgeline, the Avalanche wasn't marketed to general contractors and oil riggers; it was marketed to "sport/utility" type people...those with active lifestyles who like to bike and camp and kayak and hike. You can also draw the exact same parallel with the Explorer Sport Trac, again, also now gone. I'm not sure if it's been mentioned in this pages-long thread, but it was a true body-on-frame vehicle with good towing and hauling capability. It, too, was not marketed as a "truck", but was marketed as an alternative vehicle to those with outdoor lifestyles.
Those types of people are increasingly demanding lower emissions and lower fuel consumption from their vehicles, are turning to vehicles like the Honda CR-V, Chevy Equinox, Ford Escape, etc. Neither the Honda nor the Avalanche nor the Sport Trac failed because they were or were not "trucks", or because they did or did not have body-on-frame construction, or because they did or did not have longitudinal V-8 engines. All three had varying combinations of those qualities, and all three are now gone, or will soon be.
I believe they failed because gas prices five years ago essentially "called their bluff", and each of the automakers let the product languish. Back in 2007 when gas was cheap, sales for each of these choices were strong enough to justify their position. Through the end of that decade, however, gas became much more expensive, startlingly so for the young-to-middle age set to which these vehicles were marketed, and the demand simply went away. All three of these truckish vehicles (Ridge, Av, Sport Trac), offered the versatility of a small bed, but none of them offered good fuel economy. The cost- or eco-minded consumer was then gone. The "image" consumer is going to choose a chromed-out F-150 Lariat long before he chooses an Explorer Sport Trac, so that consumer is gone or never was there to begin with. The market simply dried up.
Honda never updated the powertrain for the Ridgeline. A brand new model uses essentially the same 3.5L engine as our 2005 Acura. One could only guess at how efficient a new Avalanche with the 3.6L DOHC V-6 might be, or how neat a car-based Sport Trac with the EcoBoost 3.5L would or could be. But all three were essentially left for dead; and it shows in the sales numbers.