Delete purchased apps from history?

This is primarily a user-to-user support forum; other Apple users like you. We don't have access to information about why not.

Also see the following if you aren't already aware of it: Hide purchases from the App Store - Apple Support

The bottom line, as far as Apple is concerned, you can't pretend that you didn't buy something that you actually bought.

M1 Mac mini, macOS 12.1; Watch, series 5 GPS/cellular, watchOS 8.3; iPad Pro 2nd Gen, iPadOS 15.2; iPad Air 2, iPadOS 15.2; iPhone 12 Pro, iOS 15.2; TV 4th Gen, tvOS 15.2; HomePods, audioOS 15.2 and Airport Express w/ Airplay 2

The Purchased List doesn't differentiate between downloading paid apps and downloading free apps.

As far as Apple is concerned, you can't pretend that you didn't download a free app that you clearly downloaded.