Why? It still works, doesn't it? They didn't stop supporting that hardware, they just stopped selling the hardware when it came redundant, since a lot of other devices can do the job (iOS, Android, Raspberry Pis and many Smart TVs can run the Steam-Link-App).
I believe they stopped issuing software updates and bug fixes when they discontinued it. It was a sudden drop in performance for me around when they discontinued it. That's pretty coincidental.