I suspect a hidden "benefit" to the companies implementing this is that it makes it much harder to share your account. You are probably happy to share your Netflix password with your mom, but not your email password.
They can present it as a "more secure" login method, obscuring the reason they actually like it.
I'm pretty sure Medium (who was the first implementation of this that I know of) uses it as a way of blocking pay wall bypassers (which on Medium I think manipulated/deleted cookies to get around the 3 article limit).
Yeah that would not surprise me, in general. I don't think that would be 404's goal, since they provide full-text RSS feeds I could share with a friend easily, but I could see that happening with other services.