Hiding names is a common practice for security.
For example, (only example) Shredderbeam decides he doesn't like R2Pleasant anymore. He finds out what the name of one of R2Pleasant's accounts is, finds a way to report the account to jagex, and the account is permbanned for breaking multiple rules. This is all because someone did not hide the account name on one of their posts.
Hiding names prevents such situations from arising.