I suppose you're right. I thought the R-44, 46 subway cars had inverters, in the 70's. As it turns out, they did, only for lighting. All the motor loads (Air, HVAC, etc, were DC)
It was a technology just starting to appear in the industrial world. I heard a story from an old electrician who was around when an early inverter (GE - the inverter division was..in Erie) was installed at a pump station...
There were three pumps, two inverters (they couldn't afford 3 - we're talking only 100 HP units here!). And a cabinet to switch the pumps into the inverters as needed. Well they made a big deal about it when it was installed (It was the late 70's - energy conservation was a BIG thing), had a big press event, invited the mayor, etc.
Naturally, when they turned it on in front of everyone, it promptly smoked out!
I remember seeing the two units in their last days. Noisy, BIG, all analog. Electrician said they never worked well. The replacements (Eaton) were so small you could pick one up. And each pump got one. Once in operation, the place was so much quieter, the office folks next door came over wondering if the pump station was being ripped out - the noise was gone!
The electrician wasn't worried about losing his job - he said a few Class Is were chasing after him because apparently the old GEs were pretty much early versions of what locomotives used, and they were desperate for folks who understood the things (what's so hard about an inverter anyway?
Today, everyone makes an inverter, and they're everywhere. Nobody uses DC in the industrial world anymore, if they can avoid it...