This has been suggested countless times since titles came out on the CLF - the main overriding issue Jagex seem to have is the potential for abuse (by making your clan name into something that avoids the censor).
There's also been a question of whether it's worth the time invested to do it, as you'd have to either have a JMod verifying all the titles before they're applied, similar to CLF access, and/or add a report abuse function/JMods to read the reports/etc. That's not taking into account the time required to code it either.
That said, it's an ongoing discussion (there's currently a thread on the first page of the CLF about it), and may happen in future in the issues around it can be satisfactorily resolved.
