This is the worst review that I have seen so far on the Titan diesel. I hope that it is an isolated case: http://www.caranddriver.com/reviews/2016-nissan-titan-xd-long-term-test-review
Toyota had to work hard to get into the 1/2t market even though it was respected in the mini truck segment. Those of you may remember their T100 entry took many iterations and changes before it became capable and renamed as the Tundra. As others have posted, the lower volume for heavier trucks makes it hard to recover development and marketing costs to enter this field even for established makes.