Why do offspec roll need on things the main need world of warcraft?

An example a dumb healing Druid rolls need on the black heart tanking trinket claiming that he is tanking off spec yes I know I'm being childish ranting on about this but at the rate the heart drops and how many Druid healers I get not to mention dps mel�e that say they are tanking spec too I do not what to do please help it is annoying I always ask if I can roll need on a tanking item if I'm not tanking wish more people did that they go as dps only to take what the tank went in there to get hard enough to get into a raid when people demand u have acheivement much less competing for tanking gear with healers and dps please tell me if there is an alternative thank you