For apps that are still 32-bit only, they have to be several years old. I believe the first version to support 64 bit was iOS 7 and at that point, I think Xcode

For apps that are still 32-bit only, they have to be several years old. I believe the first version to support 64 bit was iOS 7 and at that point, I think Xcode would compile with universal support by default. Most of our affected apps were built for iOS 6 (or lower) and the clients have not wanted to pay to keep them up to date. As a result, an update at this point requires quite a bit of work because of deprecated and removed APIs preventing us from recompiling. Then you have the issue of third-party libraries that may not support 32 bit, so you have to go find updated version (if they exist. If they don't, you have to completely remove it and find a replacement) You are correct, though, that in the best case, it is just a recompile.