

There are various designs of backlights. They typically have a stack of loose components in an assembly. By loose I mean not totally fixed but not too free. They have to free float enought that temperature changes do not cause issues. They also have to not stick, warp, or buckle over time. Harder to engineer then you might think.
So consider what might happen if for example the top backlight film might buckle some then stick to the back of the lcd. The film might deform which would change its optical properties. Then later thermal cycling might cause release. It might do same elsewhere.
Not saying this is mechanism, but just example.
Edit: Keep in mind the LCD is glass, and the backlight components are plastic. Very different thermal expansion coefficients. Then add LED or CCFL lighting and you have a big changing heat source. Add on top of that humidity changes too.










Yes good analogy. Just my guess. Been a long time since I actually worked in the field.