Nissan is coming to market with their "1500" series truck the Titan. However, that truck will probably be closer to a 3/4 ton. We're all waiting to see what the GVWR's are for that truck.
As for why we're only getting diesels now? Many blame GM for the haphazardly engineered diesels of the 70's. That has left a stigma on the market and diesels were seen as belching noisy horrible machines for many decades (Read about that in focus groups of certain truck makers). It's only now with the experience of European diesels that the american mindset has slowly warmed to diesels in lighter vehicles.
The VWAG is probably the best known proprieter of light duty diesel engines and probably has enjoyed the most success in the market as well. It's only recent that FCA has jumped on the bandwagon and is pushing the diesels in its Grand Cherokee and RAM. GM is planning on pushing a baby-duramax in the just released Colorado. If these diesels continue to be a success, you can bet more will proliferate. However, fuel prices in regions of the country are also working against diesels being more common. Depending on where you live, you can have a fuel pricing advantage with Diesel to a severe disadvantage.