Odd, I assumed that subs would run at least a few atmospheres to compensate for pressure differential. Structural assistance not worth giving the crew the bends on fast ascents?

Why bother with 2-3x more air pressure and all the problems that go with it (crew decompression, lack of abort options, etc.) when the outside pressure is hundreds or thousands of times more? You're really not gaining anything engineering-wise.

One thousand times would make it 10km depth - so clearly not “thousands”. Other than that you are right that there is no gain in e.g. doubling the internal pressure.

Yes I made a mistake in my estimation there. Max pressure at the challenger deep is about 1,000 atmosphere, so that shouldn’t have been plural.

The pressure outside is +1 bar per 10 meters. If you're 1 km deep, that's 100 bars (+1 atmospheric bar) while it's ~1 bar inside the sub. The mechanical stress on the submarine depends on the pressure difference, not the ratio. So increasing air pressure (with all the complications and risks it would bring) would only reduce the material load by a few percentage points.

Then why all the videos of people who sound like garden gnomes?

Which videos?