Interview skills do degrade. You have to practice before you interview if you haven't been doing it recently. Interviewing is a performance, it's different than normal programming, but the world mostly expects you to handle that difference.
1. You have to solve a problem immediately (whiteboard or now in a webbrowser)
2. It's often frowned upon to research via google search something, although in real life most people do it all the time.
3. you have only an hour to solve a problem, and what if you don't see the 'right and easy way' to do it? In real life things aren't so simple.
4. Don't forget it's a performance! You have to be on your best, sharpest most intelligent and witty behavior, think through things, it can be exhausting.
These are just a few of the ways that interviewing is artificial.