> What exactly did eSIM enable here?

Some examples include

* Backup service in the event that an attacker gains access to your Google Fi account. A backup eSIM with data service for a year has pricing starting at like $2.

* Fast network access in other countries. As far as I know, Google Fi is a carrier in the United States, and does not include network access in other countries.

* Deprioritized on data? The ability to instantly buy a major carrier eSIM and have the data speeds back.