When trying to access a cloud file, 'Open in Illustrator' is not an option

I am starting to work with cloud files more frequently.  When I click on the generated URL, that takes me to an online viewer of my document.  Most times, I then have the option to open the document in illustrator as shown on the right.

However, there are other times when that option isn't possible.  In both instances, I am logged into my account and the 'sharing access' settings are identical.

Why is this feature sometimes available but other times not?  If the file is shared with me, shouldn't the 'Open in Illustrator' always be an option?