If John wrote the 4th Gospel, why did he not name himself or his brother?

I've read in Ellicott's commentary that the "other" disciple of John 18:15 might be James, for it stands in contrast to John's supposed self-designation as "the beloved disciple". But that got me wondering: why did John not directly name himself or his brother within the entire gospel? Is there any church traditions or research out the that disseminates why John may have not wanted to name himself or James within his own gospel?