Matching HTML comments with Grep and Regex

I have a series of files containing html comments ( <!-- some comment -->

) which I am trying to match usinggrep

Comments only cover one line.

Here is my command

grep -rl '<!--.*?-->' ./

      

        
        
        
      

    

It doesn't match. However, if I run grep with this regex:

grep -rl '<!--.*?' ./

      

        
        
        
      

    

He works.

The original regex works in javascript, but grep doesn't seem to like it for a reason I don't know.

Thank.