Signing in lets you claim a listing that’s yours, submit a product so that approval makes the page yours, and post in the feedback forum. We read your public profile and nothing else — no repositories, no contacts, no posting on your behalf.
GitHub proves a listing is yours when it’s the account the streak was read from — the claim goes through on the spot.
Google proves it when your address is on the product’s own domain. A gmail address isn’t wrong, it’s just unverifiable, so it goes to a quick human review instead.