"Super single" tyres - pros and cons?

Ive seen a lot of trucks recently with a single extra-wide tyre on a wide rim, where there would normally be a pair of normal back-to-backs - such as the drive axles.

I'm assuming this is an economy measure as one big tyre is less cost and less maintenance than 2 tyres (and can't get debris wedged in them). If so, why are they only just beginning to appear? Obviously I appreciate that it means a) 2 different sizes of spare needed and b)a blowout immobilises the truck rather than reducing it to just limping.

Are there any other pros and cons? I'm interested in the debate