Isn't it Obvious? They're Glass Cannons. They complain if anyone is able to so much as sneeze on them.
A lot of these Glass cannon mains, (particularly the ADC mains) Don't take responsibility for their positioning that leave them in the open and waiting to get picked off. And their Squishy build, is justified by their ability to use Positioning to it's maximum Advantage. Thanks to their Range.
I target ADC's mostly Because their ability to build Life Steal makes them over confident. And consider anything that nullifies this advantage, (large amounts of CC, Thornmain, or death) to be problematic, and think they should be nerf. they also think that Stacking Full damage with Life Steal, means they can duel anyone. Which is obviously not the case.
Assassin Obviously have good ability to completely destroy ADC's, because they are also Glass cannon, but with higher Burst and better ability to commit to their targets. Personally I prefer Hard engage Bruisers. Because Glass cannons don't prioritize defensive stats, They are about as Easy to kill as they were when you had first gotten your Tri Force and your BotRK. Prioritizing defensive items, Just means you take less damage commit to the enemy ADC and will be able to continue the fight.