Reasons fro 2-staged login – email first, then password (not about 2FA)

Google changed it's login form in 2018 from being the classic login-form (email and password fields visible at the same time) to be two-staged:

• first enter the email and click next
• then on a second page enter the password; then click login/confirm

What is the reasoning behind this change?

Is it security: so that brute force attacks on known emails cannot be carried out so easily, as in the classic login forms? I've seen more and more companies changing their login forms to this pattern (evernote, micorsoft, amazon, apple ID, synology DSM, etc). Personally I find it kind of annoying as it requires the password manager to be launched twice.

Does anyone know about the why? I did not find anything useful online (except this article here)