Why can’t i back up to a google drive instead?
Why can’t I choose a Google Drive to back up my iPad Pro instead of iCloud?
iPad Pro, iPadOS 16
Because there is no option to do so. iPads can only backup to iCloud.
Why Apple did it this way, only they know, and no way for us to answer why they chose to do it that way. This is a user to user forum, and as users, we have no insight into Apple's decisions and we are not allowed to discuss Apple decisions and policies in these forums.