Another reason could be shrinking family sizes. Compared to the 80s / 90s, very few families are having 3+ kids. In large cities with much very high living costs ($1.5M for tear-down house here in Vancouver), people can barely afford 1 or 2 kids.
Then factor in how many crew cab, highly capable towing trucks are around that gets decent fuel economy and all the luxury needs you'd want.
Yes, there're niche markets with niche demands, but OEMs are after volume and profit. How many 2500 Suburbans and Excursions can they sell today? And is it purely at the cannibalization of Silverado 2500 and F250 sales?
Same reason we don't have Land Cruiser trucks, Unimogs, heavy cabovers the rest of the world gets. Lots people want them, but too much a niche market.