Scenario 1 — Older relative can't sign into Google
Your 72-year-old grandmother has no Gmail. She opens the Drive link and a sign-in screen appears.
Even with the folder shared publicly, uploading requires a Google account. Sign-up steps (phone verification, terms of use) stop grandma in her tracks.
She points her phone camera at the QR — the upload screen opens directly. No account, no password. Two taps to upload.