There are a lot more well known easter eggs in games of that era, especially in games by id software where staff would put each other's pics in hidden places in the game.

Came from a time when games were a product of passion of a few, and not of a soulless corporation.

But that's still alive in indie games today. Check out the games developed by "New Blood Interactive" for example Dusk, it's full of throwbacks and memes to classic games from the '90's. You can find them on Steam or at https://waste.money/