I'd say it's less bad design, & more a near-total lack of design. Someone needed a "good enough" way to specify target properties for a few targets they had to support, and picked a string format they could easily parse. Worked fine. Then more systems had to be added, and special cases happened, and nobody wanted to break backwards-compatibility so the system just grew. And nobody can agree on names, so people added alias support, and the system grew. And people started releasing OSes instead of just organizations so the "vendor" concept grew fuzzy, and the system grew. Now it is a hyphen-separated variable-length monster of confusion.

Ideally each component in the target "triple" would be a separate argument.