If you think about it, how many of todays average drivers even know how to check the transmission fluid? I had a guy at work try to ad trans additive to his Baja & put in the differential fill tube. So why have one when most don't know how to use it. Also it helps with revenue making as the trans either is good or dead.
Which reminds me of an old salt story: When I first got to my temporary duty station waiting for Nuclear Power School in the Navy, I was stationed aboard the USS Mahan (DDG-42) undergoing an overhaul in Philly Shipyard. I was a Machinist's Mate and got stuck in Aux Division (A-div). The old guys would dupe us young'ns by telling us to go to the boiler room to ask the boiler techs (BT's) to get a special tool called a "BT Punch" (you know where that was going). Or a bucket of steam. Well, this other guy got asked for a bucket of steam so off he went. Came back with a steel bucket he was carrying using hot work gloves. The bucket was hot as hell, and had a wet towel over the top of it. Darned if he didn't set it down in front of our leading 1st and lift back the towel and "poof", there was this big billow of steam that came out of the bucket. Never seen that done before or since. Smart fella right there. They were so impressed that they didn't mess with him again.