Appart from heat buildup in a totaly enclosed fixture an other even more severe problem kills the LED lamp.
The lamp driver is a small piece of electronics located inside the foot of the lamp or in some occasions as a separate unit and can indeed become damaged due to a to high temperature. But there is more "Moisture"
Consider an outside fixture with the lamp on in the evening. In case of an enclosed fixture the surrounding air inside the fixture is getting hot and forced out (an enclosed fixture is not damp tight). When the lamp is switched off later fresh air is sucked in again and during the night when the outside temperature drops the damp condensates leaving water behind. This water is blocked and can not escape. Repeat this action a number of times and you end up with a defective driver.
The above picture shows the result of the ingress of moisture. Similar situations I have seen with drivers inside an LED light bulb itself.
Moisture can enter enclosed fixture alongside a seal but also through the connecting cable.
Prevention can only be reached when the driver is completely enclosed with a compound at a higher cost.