I don’t work for Gainsight but I could see the reason being related to reducing confusion for Community Managers and other members. If users could change their name at any time it would be harder imo to tell who is who (of course you could find out what their email address is but that wouldn’t be apparent on the front end and take more work to piece that together). If you are a member trying to build relationships with others it might also be harder if other members are switching their names now and again.

I could also see it being a problem with open communities and spammers. They could change their name to something not blocked by the filters but still not appropriate and then change to something else before you get a screenshot. I could see even an unhappy user doing this when they know admins are not working and revert back later.

As someone who struggles with names at times, I find it helpful, even if it requires more manual work. We put a disclaimer in the registration process that we only change usernames if they believe the name is a security risk (that pesky PII). 

You’re right @jwren - at the moment, username can only be changed in the control environment at the moment.

And I second @Johnk’s reasoning - especially the spammers part. I love that disclaimer suggestion - it overall just helps hold the community stronger with some basic rules like this.