Textboard Dubs Just Aren't the Same

On image boards, there's enough traffic that you can't just notice a post number and then get dubs really easily. There's an element of luck in it, although strategic timing does play a role as well.
On text-only boards like progrider (or others), there tend to be fewer posters, and old threads aren't deleted after they get pushed back to a certain position in the thread list. You can have days, weeks, or even months to notice when there's an opportunity to post dubs. It's too easy.
When you can determine with nearly 100% certainty that you're going to get dubs, it's no fun.

The purpose of dubs is either to 1) annoy people, 2) derail conversations, 3) acknowledge something about a post that isn't actually related to the post.

Purposes 1 and 2 apply only to the posters of dubs. Porpoise 3 applies to the people that check dubs.