Exactly this. Basically the 'demand' for driving is already > than the 'capacity' for driving, so adding capacity doesn't decrease congestion, it stays at 100%. This was made explicitly clear in the crash of 2000 when it felt like roughly 25% of the work force seems to have moved out of the Bay Area, traffic congestion got a lot less.

If the theory of 'induced demand' was accurate, then traffic congestion would not have changed, and that would have been something worth writing about.