They limited it to that because, at the time, there was only one way to make a lightbulb and they wanted a consistent brightness. The easiest way to do that was to make a standard filament, and the easiest way to measure that was to test how long on average it lasted.

It is like saying a bread cartel was made by saying a loaf of bread has to be a standard weight and anyone selling a different weight was fined. Making an industry standard that is arguably for the benefit of the customer is not the same as planned obsolescence. Especially when you consider the fact that the 1000 standard wasn't followed when they started making different kinds of lightbulbs that didn't use filament.