Rewrite URL using .htaccess display 404

Question

I have a blog folder and in the blog folder, I have 2 files. index.php and post.php. Index for display all articles I write and post.php to display details about all articles. My .htaccess file has this code:

Options +MultiViews
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^\.]+)$ $1.php [NC,L]

RewriteCond %{HTTP_HOST} ^www\.example\.com$
RewriteRule ^/?$ "http\:\/\/example\.com\/" [R=301,L]

RewriteEngine On
RewriteRule ^/blog/(.*)$ ^/blog/post.php?link=$1 [L]

In my post.php I have this code:

if(!empty($_GET['link'])) {
        $id = $_REQUEST['link'];
    }

    if (null === $id) {
        header('index');
    } else {
        $sql = "SELECT * FROM blog WHERE link = :link";
        $query = $dbh->prepare($sql);
        $query->bindParam(':link', $id, PDO::PARAM_INT);
        $query->execute();
        $project = $query->fetch(PDO::FETCH_ASSOC);
    }

In the database column link have a value of SEO URL. The problem is when I open example.com/blog/ I get all articles I write, but when I open a random article, I got a 404 error, what is wrong with my code?

Note: if I change my .htaccess to this:

RewriteEngine On
RewriteRule ^blog/(.*)$ blog/post.php?link=$1 [L]

Now when I open example.com/blog/I got a details page not a list of all my articles from the database and the SEO URL works. So example.com/blog/ and example.com/blog/random-article are the same and that shouldn't be like that. Thanks for the help.