There are three possible reasons:
1. The ISP has not chosen to maintain a listing on this site.
2. The ISP does not qualify to have a listing on this site.
3. No customers of that ISP have submitted an ISP review.
There are standards for listing on this website that a lot of small Canadian ISP's don't meet. Those standards can be found here.
A company that, for example, is a pure reseller of another ISP's service, is run out of somebody's basement, or that has unresolved consumer complaints is generally not going to get listed. This ensures a high quality of listings on this site.
However, if a customer decides to submit a review on their ISP that is not currently listed and/or does not meet the listing criteria, then a placeholder listing will be created for the sole purpose of showing the reviews for that ISP.
If your ISP is not listed and you wish to review them, send the body text of the review to firstname.lastname@example.org and follow the instructions in the autoreply to complete the review.