Special:AllPages is a great way for crawlers to find the content of the wiki. To supplement that, there are the links on the pages. To supplement that, there is Special:WhatLinksHere (for dead-end pages).
However, RecentChangesLinked is very dynamic, and does not give high value to search engines in terms of links to follow, and does not give search users any value in terms of a page that will be recommended to them.
Rather than have millions of page hits to this useless page churning data that gets ignored, let's nofollow it.