Re: Why?
LED Lights are supposed to last... well forever...
An LED (and the bulbs made from them) will age over time, getting dimmer. Last I checked, a bulb was officially (U.S.) considered "dead" when it dropped to 70% of its initial illumination.
So far the outdoor lights, which are on continuously at night, are still doing fine, but they've only been in operation for two years so far. I think I can realistically expect another three years out of them, but we'll see.