Sorry no technical reason just haven't got around to it yet, didn't know what the general preference was now, will add it shortly. Thanks for the feedback
Just to give an alternative point of view - I prefer third-party login whenever it's available, so the current flow works for me. I'm not saying you shouldn't add first-party login, just don't get rid of third-party login in the process.
I don't say that 3rd party logins are bad and should be removed, I just hate when website assumes that "everyone has Facebook, Google, GitHub, <insert some other trendy site here> etc." We fought long and hard to get rid of vendor locks as much as possible, why go back to these dark times?
My problem is that I can easily create account and store it in my Keepass, however when there are only 3rd party logins I have no idea which third party login I chose to use for a specific site. This sometimes means trying to authenticate with multiple third party vendors and sometimes accidentally creating a new account as I logged in with a wrong one.
Good points there and having done that myself as well I can definitely sympathise with you. Working on the email/password auth as we speak ;)