Because Google said that the are a link scam, or a link pyramid (something like that) and that they should be nofollow. However it is actually still worth it, just not as much as it used to (also you should have a range of anchor text for it or you risk a penalty).
1) Only the first link to a webpage counts. You have 4 links to a page. Only the first one "counts" in any respect.
2) In this specific instance, there is no merit behind these links you've pasted in your signature. There's absolutely nothing telling Google that there is something of value behind these links (same goes for my signature links).
If you want links, don't waste time posting around forums hoping for your signature links to do something. Go write a quality guest blog post and leave a relevant, inline link.