The thermal management of the LEDs. If LEDs come on a standalone chip, appropriate heat sinks have to be designed to prevent premature failure of LEDs.
The electrical stress: Running LEDs at currents higher than specified make the LED run hot. This can happen with wrongly matched drivers. E.g. the driver produces 700mA whereas the LED needs 350mA stresses the LEDs and reduces its lifespan.
Higher ambient temperatures than that for which the product is rated reduces the life of the LEDs.