There are plenty of reasons to change your name that don't have anything to do with marriage. The answer to systems being inflexible and not coping with name changes is not that people shouldn't change their name. The process should be easier and less painful, and all systems need to deal with names that change, including usernames that change (since people often use part or all of their name in their username).

(Also, some people do enjoy that convention, while others do not. It shouldn't be expected, but it should certainly be permitted.)