Yes, I've wondered about all the interest in lettuce and kale. I'd expect more interest in growing higher-value seasonal crops such as blueberries or strawberries.
Lettuce can be grown at full blast and harvested in a month. For seasonal fruits there has to either be a way to trick the plant into skipping the dormant period or a dormant period.
The marijuana thing doesn't make a lot of sense to me, it's not fragile and has relatively high value compared to the cost of shipping.
It won't be legal in all the states between NY and wherever you grow it. And transporting it across state lines opens you up to interdiction/legal trouble from the Feds. That's why they have to grow it near the consumers.
The marijuana thing shouldn't make sense, you're right - intensive lettuce growing systems don't translate to hemp well at all. Height, root structure, nutrient needs, schedule, and practically everything else vary and mess up your structure.
As other people here have pointed out, they really are growing lettuce. If they wanted to be ready to switch to hemp, they'd be using a closer analogue like tomatoes.
The marijuana thing doesn't make a lot of sense to me, it's not fragile and has relatively high value compared to the cost of shipping.