Most of the established manufacturers of Blue Ray players are also manufacturers of SmartTVs, and unfortunately, when they got into the SmartTV business, they decided they could design their own streaming interface.
Although it is kind of crappy compared to Roku, they all have a mature streaming interface, and companies like Sony, Vizio, LG, etc have too much corporate ego to throw out their own system and start paying licensing fees to Roku.
The amazing rise of TCL out of nowhere has taken advantage of the popularity of the Roku system (along with competent TV design) to become one of the leading manufacturer
s!
Sharp has also adopted Roku for their TV's but IME they have glitches - the one I am familiar with takes from 15 to 45 minutes to connect to the internet when you turn it on. The TCL models don't have this problem!
But I think you are not too likely to see a Roku BluRay player until TCL (or Sharp) decides to make a BD player (which may never happen).
I think it is an idea that would be successful if someone does it! IME, replacing my Roku player roughly every three years has been a nice improvement in how responsive the streamer is. I expect to keep a TV at least twice that long, so I would expect the streaming performance/features in a TV to become outdated before I'm ready to get a new TV. I would be more willing to replace my BD player every 3 years; however, I am still completely happy with the Sony BD player I got 7 years ago (aside from the streaming "smart" aspect)!