The original 30-06 load was 220 gr so the 10 twist made sense. By the time the 308 came on the scene much lighter bullets were the norm and most manufacturers used 12 twist in 308. In fact in my experience 308's with 10 twists are pretty uncommon. Off the top of my head the Ruger American's are the only factory rifles I can think of.
While 220's aren't common anymore in 30-06, 180's are and a lot of hand loaders shoot 200's in 30-06 for bigger game. A 10 twist may still be faster than needed, but most 30-06 rifles are bought by hunters who are very traditional thinking. A slower twist 30-06 might not have sold as well as the traditional 10.
The trend to faster 10 twist 308 barrels is recent in my observation. I think this is due to the increase in interest for longer range target shooting. Remember, it isn't really weight, but bullet length that determines stability. The longer 180-190 gr high BC target bullets fired at 308 speeds can benefit from a 10 twist.
And also in my experience the average shooter won't see any issues with lighter bullets in a 10 twist. I have 4 rifles in 308 with 10, 11, and 12 twist barrels. Certain rifles are more accurate than the others, but I can't say the barrel twist is why. The 10 twist barrel shoots 125 and 130 gr bullets more accurate than the ones with slower twists. That isn't how it is supposed to work, but in my case it does.