Solid
Instead of getting readers to go through a bunch of text and paragraphs to figure out the key points,  list of reasons can highlight the main points for readers to easily take away.

Easy to gather
It’s easier for bloggers to gather a list, they can just browse around and Google what they want to write about, then put them together sometimes without any personal insight.

Good looking topic
It’s always good to have a topic starting with numbers, grabs immediate attention because it looks apart from text.

Easy to read
Similar to the format I’m using right now on this post (and most of my other posts), it’s very clean and easy to read. One key point, followed by explanations. It allows readers to go through all the points, and perhaps skip the self-explained ones.

Very RT-able
Topics like “Top 10 reasons”, “10 secrets to”, “10 Ways to”, “10 Very good reasons to” always easily get retweeted. It’s just the nature of  Twitter and users like it that way.

Less Logic
Unlike constructing paragraphs, it requires less/ no logic to put together a list of reasons.

Proven traffic maker 1
Because people are likely to share blog posts with “10 reasons” topics, they usually drive more traffic to blogs than any other posts.

Proven traffic maker 2
Because people are likely to share blog posts with “10 reasons” topics, they usually drive more traffic to blogs than any other posts.

Proven traffic maker 3
Because people are likely to share blog posts with “10 reasons” topics, they usually drive more traffic to blogs than any other posts.

And…
Yes, I did lie about the number of reasons I have, and this is what many bloggers do. Sometimes they just don’t provide true value and insight, they just try to repeat the points with different wordings to make up for the magic number 10.
Gaining traffic for your blog is a good feeling, but only bloggers who provide true value to readers, and ones who are truly passionate about what they write can get long-term subscribers and consistant traffic.