I'm guessing that they ran out of leeway with small tweaks and found that breaking inactive links was probably a better way out. We don't know the hit rates of what they call inactive nor the real cost it takes to keep them around.

A service like this is probably on maintenance mode too, so simplifying it to use fewer resources probably makes sense, and I bet the PMs are happy about shorter links, since at some point you are better off not using a link shortener and instead just use a QR code in fear of inconvenience and typos.