I'm running macOS 10.13.4 and Chirp runs just fine. However, I DID get a message warning me that it is a 32-bit app and not a 64-bit app. With 10.13.4, Apple has begun notifying users running 32-bit apps that, at some point in the future, they will not be supported. I'm not sure what the plans are for upgrading Chirp to 64-bit, but at some point, without an upgrade, it really won't run. As to why you can't get it to run now, I'm at a loss, assuming that Python was properly installed.