Just FYI anyone can download XCode from the App Store, it doesn't require a "dev login". (Agree it would be nice if MacPorts only required the XCode Command Line tools like homebrew, it would be one less download.)
I fully accept that I'm just being a complainer here, but in answer to the parents question, those are the mental blocks for me.
In an ideal world, there would be a dependency declared on Xcode for all those ports so MacPorts would work with command line tools only and fail gracefully whenever Xcode is required. However, that is currently not the case because nobody implemented an easy and automated way to tell whether a port will build fine without Xcode.