That is not always the case. Consider http://programmers.stackexchange.com/a/263542/ in which an answer was posted three years after the question was asked and two years since the last visible answer was posted ( http://programmers.stackexchange.com/posts/65281/timeline ) and is now the second highest answer in the question. That doesn't sound like 'totally ignored'.
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It does happen. In fact, I think that a couple of my best (and highest-voted) answers are necromancers. However, I should note that the question you linked has 51464 views. And a lot of the questions I've earned necromancer for were similarly well-viewed. That's not typical. Most old questions get a fraction of those views.
Edit: In fact, I should admit that I usually only put the effort into answering old questions when it's something that has a lot of views. It's an indication that the question is linked somewhere prominent or is ranking well for some search terms. Those questions are worth putting the time in for. Most aren't.
I challenge you to find a similar question on StackOverflow. On some of the other, slower StackExchange sites I can see that it might be different.