It is redundant, but for some vocal subset of the online population it doesn't go without saying. These kinds of decorations preempt comments dismissing a commenter's opinion as being privileged; for whatever reason, acknowledging one's privilege seems to avoid those kinds of comments.

It's redundant and unnecessary (and redundant), but costs very little and avoids (some) pointless internet arguments. That's why I think these disclaimers are a trend right now.