Because commenting isn't meant to generate traffic, it's more of a
by-product.

And yes, there are some things we can use to generate traffic, even
though that isn't their intended purpose, but only when it's ethical.

Leaving comments for traffic alone isn't ethical.

You're trying to take something from a community that worked hard to
get it, instead of getting credit for sharing something with a
community that you belong to, and reciprocating when it's given to you
- these are two different things.

Think about how you'd feel if someone did that to your blog, everytime
you want to evaluate a traffic method related to blogging. If you
wouldn't mind and allow it at your blog, then knock yourself out,
because whatever you are doing to others is about to happen to you.

Commenting to get traffic is also inefficient.

Why?

Let's say you leave one comment.

That comment will probably only bring you traffic as long as that post
is new. When it fades into the archives, you won't get much traffic
from it.

Let's say it's a DoFollow comment, and you're getting link juice. (A
DoFollow comment is one left at the site of a blogger who is purposely
not using the NoFollow attribute.)

Sure, your link will get followed by the search engines, and counted
among the number of links to your site, which may give you a little
boost.

But wouldn't it be better not to have to share that link juice with
the other commenters?

Wouldn't it better to have a whole post dedicated to your site?

Wouldn't it be great to get a Permanent link to your site from their
Blogroll, on a page that has more weight than a single post?

Wouldnt it be cool if someone discovered you by your link and then
shared your link with other people?

So how do you get that kind of action?

Let's look at it logically.

Good Bloggers tend to make posts about?

* Quality tools, content, services, & products that will serve their
community.

* People who are doing innovative, interesting, creative things that
will interest their community,
* Quality tools, content, services, & products that will serve their
community and make them money,
* News of interest to their community that will either save them from
doing a full blog post or help them to do a full blog post,... just to name a few.

It follows, then, that if you want a blogger to blog about your site,
to share your site with others, or to add you to their link roll, you
should :

* Make comments that will both help and intrigue the blogger and
his/her community, which make a good introduction to you.
* Form a relationship with that blogger on the basis of what you have
in common that could serve their community.
* Form a relationship with other commenters in that community.

In other words, comment to give, not to get.

If you get the same amount of love back from comments you make, then
great. If you don't, that's fine too, at least you got a link, and if
you stick to it, you'll get that love elsewhere some other day.