Because you are not all healers and all parties are not the ones you have been in. In a general sense we should encourage not eating mechanics because as other threads have shown the difference in game knowledge and skill are great, and the largest amount of people will likely benefit from learning how to play "correctly" rather than riding edges and being greedy. Both the support and the damage side.
Should we not be encouraging a higher level of play in general and a standard of at least "by design" clearing of content? What is more likely to be a standard for the majority in this game: Teaching something like "don't stand in orange and learn your rotation" or "Ok you can eat this and this but then you have to not mess up again and if you can pull off one more cast to kill this boss 10 seconds faster if you eat this and healers you should be ready to heal BLM's through any high damage even though they're wearing the worst armor in the game because they're more efficient if allowed to stand still"?