Why my comment is not shown?

I have an blog on Blogger. I want to improve my SEO, that is why I'm trying to post comments on blogs where I can put my website address. The problem is that my comment doesn't appear if I complete the website field of the comment. If the website field is leaved blank, the comment is shown. What is the problem?

Everybody that has a website wants to improve their SEO. I know nothing about Blogger but many sites (this one included) don't allow posts judged to be promoting traffic on other sites. When allowed, you get flooded with promotional posts to the point that the intended content gets lost.