Good for you but others might. Like maybe people who work their tractor where there's a higher likelihood of picking up nails, screws, etc. such as doing excavating work around new construction on a tractor which has a hoe hanging off the back. The hoe itself provides ample
ballast, and they don't want to deal with the additional weight and mess of leaking liquid when making tire repairs. I myself have had two flats over the last 14 years and I was sure glad my tires were only filled with air.
Or maybe running a 25-30 hp tractor on hills pulling a heavy 6' cutter on the back where additional rear ballast isn't needed at all and another 600# of added liquid just makes the tractor slow down and struggle that much more.
Or maybe people who use their compact tractor to mow? They remove the ballast box, FEL and they then have a bare weight tractor that doesn't rut up their lawn. They certainly wouldn't need, and likely wouldn't want, the additional weight of filled tires.