I'm not an idiomatic C# programmer, but having a text-based language is really useful in all sorts of situations:

* Interactive REPL (think psql)

* Use outside of C#, e.g. small bash scripts for automation of small tasks such as deleting old records in a cron job

* Copy/paste a into Slack, Github issues etc. without having to drag along any dependent code or worrying that it's not a complete query

Query builders are nice, but eventually they have to compile down to something "neutral" and portable.