Super singles don't wear as well.
2 less sidewalls to support the weight.
Have a blowout and you are screwed. Also, not all of the tire shops carry those things. The shop we normally use for the big trucks doesn't carry them in stock. Said they hardly sell any.
A few weeks ago, I heard an O/O on the CB say he had one throw tread, and it cost $1200 to have it changed on the road. Replaced them all with duals after that happened. Also said that for the big rigs, they see the most benefit from having SS tires on the truck AND trailer. Just the tractor or just the trailer, don't waste your money.