Why does my client have to continue with Google or enter their name and email?

The sign-in step (Continue with Google, or entering name and email to create access) is what creates your client's secure Client Portal account. That account is what lets them save progress, return later, upload documents safely, and collaborate with you on the application in real time. The email is required so the invitation and portal access can be tied to the right person, and so notifications about messages and updates reach them. It is a quick one-time step that protects their financial information.