Until extremely recently, they did offer exactly such a service, though only in a handful of markets (mine was one). They called it Premium Lite.
It was exactly what you want, a much lower priced subscription which just removed ads, and didn't include any other premium features. I happily paid for it.
We've been running Jira on prem for years, paying for server support renewals etc.
We'll likely be running on prem as long as is reasonable without support, and then moving to an alternative - maybe gitlab. Atlassian lost our business with this move.
Small feature idea: "find my ip" which zooms to/selects the apparent ip of the current visitor.