That will happen eventually no matter what so I don't think randomness is the solution either (which actually in some cases might bring one the reward actually sooner than later).

Then again, I personally haven't played this game for the game for many years, but only for my friends.
What that means is, I do things because of the fun, not solely for the reward.
In even more other words, I try to enjoy the Journey before the Destination.

Thusly, if the event is there for merely a time-sink for us to mindlessly hack on it for the reward and then just quit it, this isn't entertainment any longer, it's something completely different (and yes, I know how true that statement actually is, sadly, even though it may seem like I intend to say it is not).

That, and/or it's just badly designed but hey, who's counting at this point. ·~°;