For some reason the app supports a separate standalone window mode as well [0]. It's not clear why the developer took the trouble to support two different modes when the menubar mode doesn't seem to add anything (like a live-updating icon for throughput).
Well, I can think of one reason why it wasn't that much more trouble. François Chollet had a nice tweet [1] on why removing human cognitive friction is resulting in needless software complexity.
[0] https://github.com/darrylmorley/whatcable/blob/main/Sources/...