because:

less dangerous for tractor axles (here we have some small roads,on this roads you have too run on the verge very often, and when the exterior wheel go on the verge interior wheel doesnt have load, all effort is far from the axle, puting a big load on it)

tractor with wide wheels is narrower than with duals

you can run with less pressure in the tire = less compaction

i don't do cultivation in my row crops, and tractor which spray/plant is light enought to run narrow wheel without duals

we have good traction with wides tires

runing low pressure tires,tractor is more comfortable

we are the Michelin country, so we have been convinced of wide wheels versus duals, despite they are pricey