Like every lighting technology, LEDs degrade over time and put out less light- they just do it a lot slower than other types of lights, as long as the LEDs are properly cooled. Excess heat causes LEDs to lose brightness and fail faster than if they are properly cooled.
For LED light bulbs used in houses, the small total wattage of the LEDs means that a simple, small “heat sink” can be used to get rid of the excess heat. When you put enough LEDs together to make a high-power grow light, more elaborate cooling is required to keep the LEDs running at peak efficiency for as long as possible. LED grow lights with inadequate cooling designs will dim quickly, even though the LEDs they are made from may be rated for a very long life, because this rating requires them to be properly cooled.
LED grow lights designed with large heat sinks and fans to actively cool these heat sinks will keep LEDs cool and ensure a long life. Some designs don’t use fans but instead spread the LEDs out, which can work as long as the heat sinks are properly designed and sized, but it also places limits on the brightness of LEDs that can be used.