Claiming that "this is not a bug" sounds a lot like "you are holding it wrong".
Software that doesn't perform as the user expects is almost always a bug. Yes, these folder-packages have been a problem for years. No, that doesn't mean Apple can just leave the problem as is.
For example, try emailing an app. Doesn't work. You need to zip it first. But why doesn't Mail.app just zip the file when I select it?
Why doesn't Safari automatically zip any package that I select for uploading?
Apple came up with the idea of packages, so they better fix the issues around them. Saying that Google should fix Gmail helps no-one.
Folders yes, packages no. I often email prerelease builds of my app to people. If I forget to zip the app, it arrives broken (but i havent checked yet what exactly breaks)
I just emailed myself an app from one computer to another using Mail.app and it worked perfectly.
The only thing I can think of is that maybe your email provider modifies the message in-flight because it contains an executable. And that's something Mail.app can't possibly work around. Although if manually zipping your app fixes it then I don't know why that would be.
Software that doesn't perform as the user expects is almost always a bug. Yes, these folder-packages have been a problem for years. No, that doesn't mean Apple can just leave the problem as is.
For example, try emailing an app. Doesn't work. You need to zip it first. But why doesn't Mail.app just zip the file when I select it?
Why doesn't Safari automatically zip any package that I select for uploading?
Apple came up with the idea of packages, so they better fix the issues around them. Saying that Google should fix Gmail helps no-one.