They don't have to be always raided. There are many ways to hide your base, one of the fun aspects of vanilla.I think this would cause many problems between players and I feel like people wouldn't want to keep playing if their items are always raided
You see, in vanilla you don't build a shiny house in the grass. You make an obsidian block with your valuable stuff in the middle of the ocean, while raiding other obsidian blocks ;)
Blocks can be more or less sophisticated btw. I mean, bases.