There is no general ban on all T12's, Just a minimum efficacy with some exemptions for high CRI. There are also efficiency requirements for ballasts. None of the magnetic ballasts meets the requirements so any new fixture will be electronic.
As far as why you can still find new fixtures, that's a good question. Those new fixtures are cheap junk. I guess some people must be buying them just because it's the cheapest thing on the self.
They looked the same -- quality wise vs every other typical strip fixture. Have no idea about the ballast. They were not very expensive -- but then you have to buy the bulbs.
The last time I bought bulbs -- 8' .. I got a case.
They have crappy ballasts that underdrive the lamps. A full power F96T12 should run at 75 watts, some of the cheap ballasts only deliver 50-60 watts.
Makes it dimmer and if the power is to low the lamps won't last very long.
There are some good lamps still available, last ones I got were Sylvania F96T12/941. >90CRI and 6000 lumens. About $5 a lamp but a huge improvement over the cheaper lamps.
A standard F96T12 slimline today is 60 watts, the former 75 watt standard is tagged for cold temps, same thing happened to the F96T12/HO, 110 watt lamp marked for cold temps, former Supersaver, Wattmiser, Economiser, 95 watt lamp is the standard. Which occurred with the energy conservation act of 1992.
Still run F96T12/HO lamps in my shop, & bought a case of 110W lamps years ago, still unopened.