Blog on my shop, why Google doesn't send visitors ?

Google doesn't "send" you visitors. People may come to your site if they find your pages in the SERPs and decide the title/description that Google shows is compelling enough for them to visit your site.

So there are 2 possible issues right there:
1) Your pages are not showing high enough in the SERPs for people to find your blog pages, and/or
2) Your title and/or description doesn't encourage people to visit your blogs pages.

Figure out which issue (or both) affects you and fix accordingly.

Thank you, but yes Google sends visitors because we exactly know that Google is testing the pages and decide to show or not on the first search result page, it's not coincidence if sometimes many days in a row we have exactly the same number of visits.

If I follow your reply, how can I do so how higher in SERPs ?
I do not thinks that hundreds of blog post have a title or description that do not interest people, so the second point is not possible.

Thank you again.

decide to show or not on the first search result page

This is not "sending" you visitors. This is Google's algorithm ranking you (or not)- #1 above. It is still up to individual users whether they want to click on the link and visit your site- #2 above. The only time Google might "send" you a visitor is if a person did a search on Google and clicked the "I'm Feeling Lucky" and you were in the #1 position for that query. (In testing, I find that I no longer even see the "I'm Feeling Lucky" button as soon as I start entering a search term.)

so how higher in SERPs

- there is an entire industry devoted to this topic- you can start with our Google SEO [webmasterworld.com] forum.

I do not thinks that hundreds of blog post have a title or description that do not interest people, so the second point is not possible.

Just because you think it sounds interesting does not mean that other people would find it interesting. If you are appearing high in the SERPs and no one clicks to your site from Google, then i would say it's a very good indication that they don't find it interesting.

Another possibility could be that Google has identified your site as harmful in some way. People may click on a link and get an intermediate warning page from Google warning about your site and at that point people decide not to continue to your site. The way to verify that this is not an issue is to do a search on Google and click on some of the links to your blog posts. If you go straight to your site, it's not an issue.

I believe Google's Webmaster Tools would also notify you if it had deemed any of your pages harmful. Webmaster Tools could also alert you to any other issues that may prevent your from ranking well.