Why do some Facebook contacts not appear on my Mac/iPhone?

I've decided to try out the Facebook contact integration in Yosemite/iOS 8, and for the most part, it seemed to work pretty smoothly. However, I have some Facebook friends with actual contact information (e.g., a cell phone number or a non-@facebook.com email address) who nevertheless don't show up in my computer/phone contacts. Some of these friends have entries in my iCloud contacts with matching contact information, but they still aren't matched to their corresponding Facebook accounts. How can I get these Facebook accounts to show up as contacts on my Mac/iPhone?