It's in Chrome, Firefox, Safari, Windows 10, macOS because it efficiently solves a huge number of use cases while giving plenty of headroom for flexible querying.

If you have data more complicated than a single CSV or tab-separated text file that you will only ever process in sequential order, and you don't need inter-process interaction, you should be asking why not use SQLite.

sqlite is useful everywhere CSV files are useful but you'd like them to have more data integrity and faster updates. sqlite can replace some uses of MySQL, but more commonly it replaces fopen. https://sqlite.org/whentouse.html

Quite a bit, it seems: https://tailscale.com/blog/database-for-2022