10,000 miles per year at 10 mpg = 1000 gallons of gas
10,000 miles per year at 20 mpg = 500 gallons of gas
10,000 miles per year at 40 mpg = 250 gallons of gas
You save 500 gallons going from 10 -> 20 mpg, but only 250 gallons going from 20-> 40.
Of course it's best to use the highest mpg you can, but the benefit drops proportionally as it gets higher, so it's harder to justify the extra expense when a lower mpg vehicle (but still relatively high) might be much less expensive to buy and maintain and possibly even have less environmental impact to manufacture. After all someone has to mine the Lithium etc. in all those batteries.
The trucks and SUVs in OPs post are both more expensive and more material intensive than a 35 mpg sedan. I agree with you about the tradeoff as you go up the mileage scale from there, but there are lots of medium sized vehicles that just destroy trucks and SUVs on those metrics.
Just put up the instantaneous-mileage screen and you'll see how hard it is to keep it in the higher range.
Of course, this isn't a fair comparison. Personally, I'd love to see much wider use of HOV lanes, possibly with a steep up-front permit cost for people who refuse to carpool. (By the time this happens, though, we'll probably all be using just-in-time self-driving cars.)
Which is comparable, but it also ends up being an extra gallon of fuel every 100 miles (on a base of about 3 gallons per 100 miles).