The reason for this, as I understand it, is that it's super easy to make a lightbulb that lasts 30 years. But there are two main trade-offs that make it bad for consumers:

1. Stronger filaments that last longer will be a lot less efficient, so the consumer ends up using a lot more electricity.

2. The filament doesn't burn per-say, but actually evaporates. This is why it'll eventually break. But where does the evaporated metal go? It condenses on the inner surface of the glass, making the lightbulb dimmer than when it was new.

So 1000 hours is a good middle ground. The lightbulb is fairly efficient and 1000 hours isn't long enough for the inside of the glass to get too dark from the condensed filament metal.

Price of the bulbs was also reasonably low. It's cheaper to change out a lightbulb every 1000 hours than the electricity costs of a 10 000 hour lightbulb that emits the same amount of visible light. I don't have hard numbers for that, but it's my understanding.

Watch the youtube video linked by one of the grandparent comments. It's super informative and also contains some experiments to show the trade-offs.

I really don't see this as a debunking of the idea that the cartel was set up primarily to increase profits among its members. The engineering tradeoffs make sense, but it doesn't follow that because of these tradeoffs, the companies manufacturing lightbulbs were compelled to set up an organization that fined its members for making bulbs that lasted too long. The tradeoffs explanation seems like a post-hoc justification for something that was clearly done with anti-competitive intent.

Ultimately which scenario makes the most sense: that these businesses went through the time and effort to set up this testing organization out of a desire to ensure they all made better products for consumers, or out of a realization that they could all stabilize their revenues if they all sold products that would need to be replaced on a regular basis?

This also strikes me as an area where consumer choice can be particularly effective: most of the attributes of a lightbulb aside from energy consumption are pretty tangible to the end user, and since they are fairly inexpensive and replaceable, the buyer is more able to evaluate them side by side than many other things. It makes total sense to me that the manufacturers would see this as a problem, and choose to limit consumer choice instead of competing to make better products.

This is a both can be true situation. Its legacy was a cartel oriented around protecting profits, but the coordination nevertheless also reflected an array of engineering compromises that made sense. The situation we have now is that those compromises continued to have a rationale beyond the existence of the cartel.

If I remember right from the last time I looked into this, they also fined members for making bulbs that lasted shorter than 1000 hours. The goal was a standardized product, largely to protect regional sales agreements rather than any specific concerns about long bulb life vs sales.