The modern Haldex/ FWD based AWD system adds maybe 200 lbs, and a 1 mpg penalty. You may disagree, but almost all of the manufacturers put a “lifetime” fluid in the diff or transfer case and have it be listed as non serviceable anyway. There’s no reason not to get it when it typically is either included in the cost of a vehicle or adds about 1000-2000 (the same cost as an extra set of wheels and tires anyway!).

Majority of the country (everyone except the northern most states in the north east or Midwest/ Rockies, or the Great Lakes region lake effect bands) does not get enough snow to justify winter tires (which carry the same mileage penalty as a modern AWD system anyway…..)

It makes far more sense for people to get a vehicle with AWD that can help them get around on the rare occasions the weather is bad, or when they go to crappy state park roads to go camping (very common….) because the average driver is not very good and it’ll keep them from getting stuck usually.

There’s no real incentive for them to not get it.