Basically, there is a code included in blog platforms that discourages crawling bots from following comment links. Remove the code and everyone commenting also gets to benefit.
The code was placed to help prevent spamming but there are now other ways to moderate spamming. Check your blog settings and click on your options for comment moderation.
I recommend reading the following links for further information and for instructions on how to remove the offending code thus supporting your blogging community. I also like Dawud Miracle's informative article. Check it out.