Let's go look at FFXI, specifically the endgame events:

Dynamis: All trash mobs dropped Relic AF, currencies, and rare crafting materials, which are required for relic weapons. Some even extend the time limit duration in Dynamis.

Limbus: Every mobs dropped limbus currency, which are highly valuable, and can be sold for a lot of money, or used to buy rare gears, that can only be purchased with the said limbus currencies. (Aka Ancient Beastmen's coin.)

Salvage: You enter with extreme status/gear limitations. To fix this, you need cells. what drop cells? Mobs.

Sky and Sea: Most mobs are skipped via sneak or invis, or people just avoid them if they are true sight, and generally go directly to boss or targeted mobs that are part of the NM system chain. However, some mobs have to be fought to farm key items to sub bosses for the primary bosses.

Considering that a good majority of FFXIV players also played FFXI, and hell i'm willing to bet that many of them even participated in any of these events. IS it REALLY that surprising, that people feel that it's unfair to kill trash mobs that give absolutely no benefit whatsoever? Again, please don't even try to say "BUT OMG YOU GET ACCESS TO THE BOSS", it doesn't really fly.

Face it. you would be doing the same thing if you're in the position to.