I think there are two main areas where we improve the default experience.

1. Zero configuration needed to get started.

With Fig, the experience just works out of the box. A lot of developers - especially people less comfortable with the terminal - don't feel confident installing a bunch of 3rd party zsh completions or creating a custom setup.

2. Extensibility.

We've worked really hard to make the experience of writing your own completions very easy and powerful. Lots of teams are using Fig to make internal scripts and CLI tools more ergonomic and discoverable.

In my experience, writing custom shell completion scripts is not very much fun.