Trash isn't worth killing to get to the boss if you're able to bypass it. Trash exists in this game at 50 solely to slow things down and run up repair bills.
It's not that people want something for nothing, it's that they don't want nothing for something (kill enemies for absolutely no reason to get to spend money fixing your gear... no thanks). Even if trash dropped enough gil to cover the costs of killing it, that'd be something.
And yes, trash is absolutely a time-sink. It's a filler activity of no value specifically designed to lengthen the duration of a dungeon. Low-level dungeons give very decent XP for killing trash, which is plenty of incentive. 50-cap dungeons obviously don't give XP, but the XP isn't replaced by anything else, so it goes from an activity with value to an activity with none.
SE had the opportunity to make the trash in 50 dungeons worthwhile and elected not to. It's a shame, really, because people are just going to keep looking for new ways to bypass the filler content to maximize the valuable content. If speed running wasn't an intended gameplay style, then they should give you a reason not to speed run, not simply try to outsmart a big group of people who don't want to be bothered with filler.