Why doesn’t exist for iPad Air 1? Would love it

Because the 1st gen iPad Air is now almost 7 years old and it's internal hardware is too outdated and incompatible with current versions of iOS. It lacks the right Chipset and the right amount of RAM.

The 1st gen Air couldn't even support iOS 13, it's stuck on 12.4.8.

If you want iOS 14, please buy a new and current-gen iPad.

Why doesn't "what" exist for iPad Air 1? If you are asking about iPadOS 14, iPad Air 1 could not run iPadOS 13, so there is NO WAY it will be able to run iPadOS 14. If this is what you want, then it's time to retire your very old iPad and get a more modern one which can run the newest software.