Why would that be? The warranty is against defects in the product(design or manufacturing) that prevents you from using it for the expected lifetime. Limiting it to way shorter period than the lifetime doesn't feel right.
I didn't investigate too much when I was hit by this, but apparently it's because these kinds of goods suffer from wear. Now obviously, it doesn't make much sense to allow a manufacturer to advertise 10k hours for a lightbulb while only offering 6 months of warranty, but here we are.
For a laptop battery I might have put in more effort to dispute with the manufacturer, but for two ~5€ lightbulbs I just couldn't be arsed.
