Due to my sloppiness in reviewing, I've been blocked from reviewing for a while. However, on my home page, I'm shown a non-zero number of items to review. Why?
Because the number of items doesn't depend on the user seeing it. It's the same for everyone. It doesn't change if you've done all the reviewing you can do in a day, and it doesn't change if you've voted for everything in the queues so can't review anything else and it doesn't change if you're blocked from reviewing.
This is explained in the main meta here:
It is also cached, so may or may not be very accurate depending on the amount of ongoing activity in /review at any given time.
Basically, the number shown isn't the number of reviews you can do, but the number of review items for the entire site.