Thanks. The drive train point makes sense if it's mechanical or hydraulic/shaft drive. You don't want to drive the transmission backward without lube pumps working while in transit. If you're going to tow a car with an automatic, you need to remove the drive shaft (rear wheel drive) or get the drive wheels off the ground for the same reason. The transmission oil pump only works when the engine is running.

For those old-timer nitpickers, yes, there were a few automatics with both front and rear pumps, which could be flat-towed for moderate distances at limited speeds. The old (2-speed) Chevy Powerglide was one of them. Such transmissions haven't been built for many decades.