Two ways I can see as an outsider: 1. Google Drive/One/whatever subscriptions to pay for more storage if you want to keep your old emails/files in their cloud.

Two ways I can see as an outsider: 1. Google Drive/One/whatever subscriptions to pay for more storage if you want to keep your old emails/files in their cloud. 2. Keeping people signed into their Google account for email could make them easier to track as they're also identified/signed in elsewhere on the web.