Brand recognition likely plays a big part in it. Toyota 4runners, Tacomas, and Tundras (plus the LC) have a lot of recognition in the offroading circles. Nissan also hasn't been doing a good job of marketing itself to the SUV/truck buyers:
- The milked the last gen Xterra for everything it was worth for 10 years straight without really changing anything, until they let it quietly die with no replacement....not a whole lot of effort to win over consumers IMO.
- The early Xterra's had transmission fluid issues (SMOD), and the rear leaf springs sagged over time. Even though those issues were either resolved or had quick fixes, the perception was that Toyota's equivalent (the 4runner) was better.
- They flipped flop back and forth on the pathfinder, first transitioning to unibody in the 2nd gen, then back to BOF with the 3rd gen (but independent rear suspension for some reason), then back to unibody with the current gen (essentially joining the ever increasing ranks of car-based cross-overs). Nissan just never seemed committed to marketing the pathfinder as a hardcore, robust offroader in the same way the 4runner or Jeep Wrangler were marketed.
Nissan I think made a good move by putting a smaller Cummins in the current Titan, so we'll see how that sells. But they pretty much quit the body-on-frame SUV market, which is a shame.