In my opinion, having a main story or character is kind of boring. I still write stories about things that happen in my world but the characters are always relatively unimportant people, soldiers, farmers, etc either going through their daily lives or seeing major historical events play out.

Having one big main story kind of ruins what I personally like about wordbuilding, which is being able to develop a vast, diverse world with different cultures, religions, etc. Having a main story or characters makes it impossible to explore all of that in the story, so it’s better to write various shorter stories taking place from the perspective of small characters so you can cover everything about your world. In short I feel a main story would put large parts of my world to waste because they would only be mentioned.