Comment by crazygringo

Because it's too dependent on business logic.

Different products will handle soft deletes differently. Which queries need to include soft-deleted rows and which don't? What about different levels of soft deletes, e.g. done by the user (can be undone by user) vs. done by an admin (can't be undone by user)?

Implementing soft deletes yourself isn't hard. Yes you'll have to make a bunch of decisions about how they work in every circumstance, but that's the point.