Recently Facebook decided to hide all other e-mail addresses but your @facebook.com address on your Facebook profile.
After all, Facebook is a free service, so you should consider yourself "the product" rather than "the customer". Facebook’s real customers are their advertisers and not you, so they can do more or less anything with your account and all you can do about it is to cancel your Facebook account if you don’t like it. Annoying but that is how the free services works ("you get what you pay for" and "there are no such thing as a free lunch" and so on).
It is a bit irritating but easy to fix. This is how you do it:
- Go to your Facebook profile page
- Click on About
- Scroll down to Contact details and click Edit
- Click on the small circle to the right of your @facebook.com address and select Hidden from timeline
- Click on the small circle to the right of your preferred email address and select Shown on timeline
- Click on the Save button in the bottom of the popup box