I think in at least some instances of projects like this, the goal is not really "traffic reduction", even if that's what officials publicly claim to sell it to the public. As you say, the phenomenon of induced demand is well known & presumably the people involved in driving these projects are aware of it.

The goal is increased throughput/economic activity. If it takes X time to get a vehicle from A to B, and then you add lanes & demand goes up to keep X relatively constant, that can still be a net gain for community. It's about as equally frustrating for the folks sitting in traffic, but there's still more vehicles getting from A to B because there's more lanes, and more vehicles moving around can be good for the local economy.