Why is my computer taking away disk space when I uninstall programs?

What operating system are you using? I am going to assume Windows but I would like confirmation.

Yes, windows.

It might be worth looking in programs folder to see if the uninstall program actually deleted the files.

I don’t know why this happened, but a couple of utilities will probably help.

Disk Cleanup is included with Windows
Disk cleanup in Windows 10
How to Use Disk Cleanup in Windows 7 and Vista

Revo Uninstaller does a more thorough job of removing associated files than many self-uninstallers. There is a free version and a Pro version. I’ve used the free one without wishing I bought the pro.
Revo Uninstaller

Perhaps check your programs folder in file explorer to ensure that all components have been deleted.
The uninstaller won’t always delete everything, usually, a pop-up will appear with notification that this is the case but perhaps it can occur without notification as well.