Jeep wont build a truck, because dodge makes them, and it's a bad idea to take sales away from one of your own companys, by selling the same product with a different name.
Correction: Building a Jeep full-size truck is a bad idea, because it will cannibalize Ram sales.
For example, if the Gladiators/J-Series trucks followed the same evolutionary path as all other full-size pickups, you'd have some fairly generic full-size pickups that would compete in the exact same market as the Ram. Maybe they'd come with solid axels and some extra off-road ability in all sizes, kind of like a miniature Power Wagon setup, but, essentially, Rams with 7-slot grilles. However, then there'd be millions and millions wasted in extra tooling, promotion, infrastructure, R&D and so forth required to build and sell them, which would, in turn, bring down the profit margins at Ram as well-a lose-lose situation all-around.
HOWEVER, if Jeep could build a pickup that takes advantage of exiting production infrastructure and doesn't compete directly with Ram, then you'd have something-and the Gladiator concept does that.
Here's what would you'd need to offer a new pickup in the market:
-Small or Midsize-Full-size pickup buyers are the most loyal consumers in the industry-commercial buyers who buy large fleets of them generally have an infrastructure canted towards one brand, and, unless they have an epic failure with that brand, they're not going to change. Same is true for private buyers-people buy a full-size truck because they owned the earlier version and it worked well, or they grew up with that version and so forth. If you take a look at the sales history of the 3 main full-size lines, they've held virtually the same market share forever. The Ram grew a fair amount when redesigned in 1993, and all lost a little when the Titan and Tundra came out, but it hasn't changed much, ever.
Midsize trucks, however, do not have as much loyalty. Midsize truck buyers are either very practical, who will shop around for the truck that best suits them as opposed to simply buying what they've always owned. In addition, the market is very flexible-buying trends change from truck to truck very rapidly.
-Off-road oriented-Currently, only two truly dedicated off-road trucks exist on the market today: The Ford SVT Raptor and Ram Power Wagon. Both are also HUGE. Being that we're talking about a Jeep truck here, it's a no-brainer in this department to boot.
-Crew Cab/Extended Cab-Outside of fleet sales (Which, granted, are large), single-cab trucks are on the way out. Extended Cab option is a minimum.
-Diesel-Nobody offers a small diesel pickup in North America, but the demand is there. Mahindra plans to capitalize on this with the TR-20 and TR-40, but Jeep, being a MUCH better known brand with one of the strongest and most dedicated followings in the industry, could both take a large segment of that market and attract plenty of people who'd never even consider a Mahindra.