I felt the same way, and made my own package for adding slog attributes to an error for easier logging. It's usually all I need for my own custom errors.

https://github.com/Danlock/pkg/blob/main/errors/attr_test.go

I can understand why it's not in the stdlib though, it seems easy enough to run into key overwriting issues if a dependency returned custom errors with attributes.

I appreciate the built in support slog has for slog.GroupValue and the slog.LogValuer interface that enables everyone to build a solution best for their needs.