The "etc" is pretty important here. You can log in using Reddit, and you can create a random throwaway Reddit account without filling in any other details (no email address or phone number required).
I believe they no longer allow new accounts without an email address.
It used to be that reddit had a user creation screen that looked like you needed to input an email address, but you could actually just click "Next" to skip it.
The last time I had cause to make a reddit account, they no longer allowed this.
I'd guess they push you to their content for the same reason they make that content in the first place: they believe you'll like it and keep watching it.
Ad placement is one wrinkle that would incentivize promoting their own content, but I don't get the impression that's big enough to make the difference at the margins.
If they successfully steer you towards Netflix produced content, you're less sensitive to what happens to the licensed content.