Email because that's what people are use to.
For me personally I'd just have that "Login with Keystr" button only, but the rest of the options is for the masses.
Discussion
You still need an nsec to sign. Where does email fit into this? Recovery?
The nsec get regenerated everytime you use the same email with the same pass and/or lock. And like what we have now, the nsec is stored in the app once added in, purged once you log out (added back again, the same nsec, once you use the same email pass lock combo to regenerate the same nsec)