Someone recently asked this question on Quora:
I have noticed a trend in grammar where what was once regarded as singular, now is expressed in the plural. Is my perception correct and, if so, do I simply acquiesce?
If you do acquiesce, you have some cover.
The International Writing Centers Association recently adopted a policy of allowing plural pronouns to replace the clunky “he or she” and “his or hers.” This acknowledges how people actually speak and also reflects the increasing recognition of non-binary gender identities.
Political conservatives would probably endorse the former reason, political liberals the latter.
Anyone who gives you a hard time about it probably worries too much.