I'm just chiming in to say that the fact that the lifespan of 1,000 hours continued to be standard for many decades after the cartel was dissolved should be the big sign that the limited lifespan wasn't that nefarious.
Remember what an incandescent light bulb is. It is far less glass than a jar of jam, a few tiny little support wires, and a little bit of tungsten.
Once machines were building them, they cost pennies.