I have at least 2 GC's and several other 'pro audio' stores within 90 minutes of me and they all have passive and active equipment.
I also like cowboy boots and know alot of people in the Country line dancing universe - and they are not buying square toe cowboy boots.
Trucks .. here's Ford's website -
2019 Ford® F-150 XL Truck | Model Highlights | Ford.com - (https://www.ford.com/trucks/f150/2019/models/f150-xl/) - kinda looks like a single cab to me. You can also get a 250, 350 and 450 in single cab configuration and if I had to guess, with a bunch of amenities.
Chevy sells the Silverado 1500, 2500 and 3500 as a single cab. I'm almost certain you can outfit these any way you want them as well. Ram will sell a 1500, 2500 and 3500 in single cab configuration. Nissan - Titan offers a single cab. Toyota does not offer a single cab any longer. Pickups are no longer just a work truck and a dealer will generally not have in stock what's not selling - but you can absolutely buy a single cab from most MFR's.
While 16" wheels on a pickup don't seem to be available from the Ford factory, 17's are - and that's smaller than an 18". The rest of the lineups .. Chevy 17", Ram 17" and Nissan 18". You might be able to find 16" aftermarket (if you really wanted them) but you'd have to make sure that they clear the bigger brakes and other things. If I had to guess, this is also due to carrying a heavier load - and the wheel size does impact the vehicle ride.
All the 'fancy' trucks are double cab or larger because that's what families are buying - it's not where MFR's are steering us .. much like alot of stores are closing because people are buying online. WE are forcing some of these stores to close by not shopping there.
Back on topic, the first truck to do away with single cabs was the Tundra - because 0.4% of total Tundra sales were single cab, followed by 34.1 % for double cab and 65.5% for crew max. This means if you built 1,000 single cabs, 4 of them sold - and from a financial aspect, that's terrible. Again, it comes down to what people are buying. If all MFR's took away every configuration and left you with only single cab, then they would be steering you toward a specific configuration. As you can see, most MFR's still offer various cabs anda variety of wheel sizes (17"-20") as of January 12, 2020.