Not even just raids. Back in BC near launch my server basically had a shit list for people and they would just get ignored when people were making heroic groups. You afk or half ass something, you ruined your reputation, and no group worth a damn would take you. Now you queue into people you likely never see again so a lot of people can't be bothered.
The result is the OP's issue. People know they can still get a group next week no matter what they do this week which means most dps don't give a shit. Then you have the tuning that allows you to beat the encounter with most of the dps dead on lfr/flex which again makes it less likely the dps will give a shit or that people will give a shit about the dps. Sadly, in the name of 'seeing the content,' this behavior has become accepted and expected. The tank on the other hand you still need to do stuff which is why people actually care and bitch about the tank. You can't fix that until you either have a way to make people responsible for their actions by being black listed by the community or by making the encounter impossible unless the dps play to the same standard as the tank. The former doesn't happen because of random groups across all servers, and the latter doesn't happen because LFR and really Flex too have to be tuned to be super easy so that people can 'see the content.'