Much of the code needs nothing more than a recompile. It’s just no one is doing that.
To run 32 bit stuff you need copies of all the system libraries. You lose a lot of RAM to that. You have to continue to ensure they don’t have bugs. All for apps that are abandoned.
I totally understand what apple is doing. I bet you a ton of those apps were never updated for iPhone 6 screen shizes either.
You would only lose the RAM and the disk space if the 32bit support is actually needed and installed. What’s better - having unused RAM and your app refusing to launch, or using RAM to run your important legacy app?
Due to these updates I don't know that they would still run on Windows XP but it's nice that the code hasn't needed to change.