March 26th, 2015 at 11:06am
Aside from the possible explanations below, I'll add that I think some subscribers are users who solely use the site to read stories on (and subscribe to get email alerts for updates), so they don't do anything else with their account including rec'ing stories.
There are probably quite a few reasons that make someone only subscribe, but at least there are plenty of people who do rec stories, as well as the commenters, that we can be grateful for
Sometimes, recs don't go through. You click the button and nothing happens. It's the same with subscriptions, but it's somewhat easier to tell if that went through because you'll see the story being updated in the story page and wonder why Mibba didn't tell you it was updated :P