Names are not unique so it doesn't allow for sending by name. Username is always unique. Your usage makes them unique, but that's self imposed. Ideally you shouldn't use Name at all and set your IDs as the Username.
Sending by name maybe allowed in the future, but I've no idea when as it'd need a search functionality to handle cases of multiple users with same name. Have added a feature ticket for this below.
forge.joomlapolis.com/issues/8199