What you maybe want to hear is, that there are some reasons why green LEDs might have shorter lifetime, inherent in their physics. Green LEDs are prepared from widegap compound semiconductors like AlAs and GaP, which tend to have indirect bandgap. This means much lower efficiency, hence more energy converted into heat, which in turn means reduced lifetime. They also need to be heavier doped, which may cause unwanted defects. They are also lattice mismatched to common substrates (AlAs on GaAs) which means strained layers (read: potential troubles) or the substrate tends to have more defects for more problematic processing (GaP). There are possibly also other more modern processes stemming from the blue-LED quest (SiC?) - I don't follow it any more unfortunately - but they certainly have their own quirks.

But, frankly speaking, there is much much more which can go wrong on the way from "pure physics" to the lamp "on the street" - and I believe they are as much responsible for the possible failuer as the raw semiconductor... Device processing, system design, mechanical and thermal stress - all sort of things that can and does go wrong...

JW