The issue with signing up with Lightning was that it wasn’t uncommon for people to lose access to their accounts. This could happen if they switched wallets, used a custodial service that disappeared, or simply forgot the wallet they used to authenticate.

You can still link lnauth in the login settings and people can still login with lnauth. It's just a noobchaos prevention measure, people that want lnauth can still get it. More details here