Where do you get that idea. The vast majority of pickup trucks have 6½ beds, the exact same as the Tesla. Some are smaller, and some are larger, but today most people opt for a club or crew cab and a 6½ bed.
I have no idea the dimensions, the bed just looks small from the photos. This truck isn't geared toward blue collar workers or rural folk (who don't care about EVs and want gas and won't have the access to charging infrastructure as much anyways), they wouldn't touch this futuristic design with a pole, it's geared toward Marty McFly and urban hipsters, but i don't care i'd like to see it on the road because it looks cool and hilarious.