Google's going to war with Roku over something that Google doesn't care about at all (it's one minor ancillary line of business to them), but is Roku's main and only meaningful line of business.
If you want to be locked into a single vendor, you can already buy Google TV from Sony or TCL (where this vendor-lock-in is guaranteed). The whole point of Roku is that it's independent, it's not operated by any one streaming/media service, it's not a "Google TV" or an "Apple TV" or a "PlayStation TV" or whatever.
Roku has to fight this, tooth-and-nail, or all other services on the Roku platform will demand the same, and totally destroy the entire Roku product lineup.