Another similar example, blowing into the microphone would spin the title name around on 3ds games (and poking/blowing at random things in game would sometimes do fun stuff too!)
Those tiny details and fun little things here and there are what people remember in 10-20 years. I wish developers did them more
I suspect these things happened because of waterfall development style. If you finish the product with time before the launch date, you can add in some fun.
Now, everyone uses Agile-ish, and software is NEVER finished. You always have a backlog. Those are always going to be more important to your PM than an Easter Egg.
Those tiny details and fun little things here and there are what people remember in 10-20 years. I wish developers did them more