Why do some sites call the entrance to their account "Log in", and others "Sign in"?

Question

IT terminology

Why do websites call their login "Log in" and others "Sign in"?
For example, Facebook and Instagram log in to an existing account - Log in
Google and github log in to an existing account - Sign in
Why is there such a difference? Do these phrases have different meanings?

Answer 1

In general, if you are a complete perfectionist, then "log in" is more like "enter", and "sign in" is more like "register". But since far from all perfectionists, they write how the left heel will tell to whom at a particular point in time without making any special distinctions.

Answer 2

Because they can.