What? If every English speaker does it, then it is standard English. There is no absolute standard of correctness outside that established mutually by all native speakers. (Of course, native speakers make mistakes, but when they repeatedly do it this way, and their listeners accept it, and it appears in published writing, then surely it's an established usage).
Would it be correct to say "the agenda is packed" even though "agenda" was originally plural? No, because no-one uses it that way. Equally, "data" as singular is a widespread consistent usage.