There are times when I am questing on a gatherer and just want to go mine/herb instead of questing. I set my hearth where I am questing so that I can easily get back to that spot once I am done gathering. Although you may think they are useless, a lot of players use them for different reasons.
They are very useful at speeding up the leveling process especially when a quest has you run pretty dam far just to complete it.
other than that some people might just prefer to hearth to a different spot than a major city, and not to mention as has been said before there is always flight paths and flying mounts that can get you anywhere in a couple of minutes.
The questing style was kinda different back in the old world
you didnt really have much of a reason to go back to major citys when you was leveling up so you would set your hearth to a questing hub so when you completed the quests you could easily get there without having to run back cause you didnt get mounts till level 40 and epic mounts till 60 plus the FPs had to be discovered for you to use them
IMO innkeepers do seem to be quite useless these days but i see no reason to get rid of them