That’s because they’re hidden, but luckily they’re very easy to get back.
Just navigate to Settings > About phone or About tablet. Find the build number at the bottom of the list (JOP40C in the case of the Nexus 7). Tap it seven times in a row, and when the settings are successfully unlocked, you’ll see this message: “You are now a developer!”
The developer options are now back where they belong. (Try to tap the build number again, and you’ll get this: “No need, you are already a developer.”)
Most likely, Google hid these as inexperienced people were probably tinkering with them, messing things up, and subsequently complaining. Now, as the Nexus line grows in popularity, there is a smaller risk that people who don’t really know what they’re doing will do that again, although they’re still easily available to those who want them. Kudos, Google.
[Android Central]