Two things about that: Pros also don‘t use the 11-tooth cog on the flats either, nor do they use the 12-tooth cog. Just have a look at the speeds you can reach with either, pros choose chain rings so that their chain line is as straight as possible and gears that are as large as possible when they are cruising. They want to maximize efficiency in the gears they use the most. But I reckon the extra gear they have on a SRAM-equipped bike will still be helpful when going downhill, and the fact that it has 10 teeth won‘t matter much.
The second thing is that most people are not pros, and what is best for pros is often detrimental for ordinary or even very fit riders. The 10-tooth cog is usually only used when you are going downhill, and then I doubt the loss of efficiency matters much for the average rider. What you gain is much larger range, which is something every rider can appreciate. IMHO road bikes are ridiculously overgeared for most riders. I‘m reasonably fit and my lowest gear is a 40:36 = 1.17, and I sometimes have to grind even though I put out a decent amount of power when climbing some hills (think 300–400 W). On the top end (42:10 = 4.2), I can pedal until 60–65 km/h, which is plenty on public roads and all races I have participated in.