Because it's cheap to replace a roku/chromecast as technology evolves, but TVs tend to be longer-term investments. Hating smart TVs is akin to hating cars that have built-in factory navigation systems. Content streaming devices/services (and mapping/navigation/music for cars) regularly evolve/change with the fast pace of technology and the Internet, while TVs and Cars are hardware you hang onto for a long period of years. You don't want outdated tech baked into your hardware forever, especially tech built in by companies that don't specialize in that stuff to begin with.