Why doesnt Apple allow the complete removal of apps not only from the home screen but the app library as well?

You can definitely delete apps.. including from the App Library.

'removing' is a term that is different then deleting.. removing will just remove from Home Screen, but it will still reside in the App Library.

Remove apps from iPhone - Apple Support

However, there are some built in apps that you cannot delete

Delete built-in Apple apps from the Home Screen on your iOS 14 or later or iPadOS device or Apple Watch - Apple Support

review this support article (looks like you came here from this article)

How to delete apps on your iPhone, iPad, and iPod touch - Apple Support

• You can delete an app from your Home Screen by tap/hold on the app icon, when the menu pops up, select Remove App, then in the subsequent menu select Delete App
• You can delete an app from the App Library by locating the app and tap/hold, select Delete App.
• You can delete an app by navigating to Settings > General > iPhone Storage > [app name] scroll all the way down to the bottom and select Delete App.

--> If you are unable to delete apps with any of these methods, check:

Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Deleting Apps

make sure that's set to 'Allow'

"Why" questions can only be answered by Apple. On this user-to-user support site, we are all users......just like you. No one here can explain the thinking or decisions that have been made by Apple.

If you want to make some suggestions to Apple, you can do so by clicking on this link:

Feedback - iPhone - AppleApple › feedback › iphone