Unlike Tesla, GM doesn't own its dealerships. Each dealership tries to optimize their selection for their own profit, each salesperson to optimize their sales for their own income. There's a complicated web of incentives tweaking which models are best for which entity at which time, but as a general rule if they are relatively inexpensive to manufacture and/or there are lots of them in inventory that's what they want to sell you. Trucks and those SUVs built on truck frames are always at the top of the list (Ford's F-150 is rumored to be the most profitable vehicle ever built, I think the Escalade is among GM's most profitable vehicle). If someone can create a cheap to build electric truck it might well grab the interest of dealers and salespeople, but they're never going to be excited to sell you a hard to build, low-margin family sedan regardless of powertrain.