In most species males compete for access to females, but in these insects things may be the other way round — because males are a good source of food. (newscientist.com)
These males don't have exclusive access to females, and the battle for reproduction is geared more towards «sperm competition»: quantity and quality of sperm. (sciencedaily.com)
According to this hypothesis, it was advantageous for males to remain short because it gave them an edge when grappling with one another for access to females. (discovermagazine.com)