[menzoic]

There's a cost to developing features. "Just let me use email" is dismissive to the fact. 99.999999% of users will be able to use one of those. Why spend more time making a subpar email login feature when you can integrate with existing services that probably even increase sign up conversion because it's an easier UX?

[muratsu]

Because target users are developers and developers don't like using social logins as much as other users. Using firebase or 0auth is pretty straightforward as well.