there are other streams with input of hatchery coho that are not open to salmon fishing... Burnette creek in New Westminster/Burnaby is another example.
As I recall the reason why all streams and rivers in Region 2 were initially restricted to no fishing for salmon was that DFO had been unable to do stream assessments for many years and had no idea of what condition the various runs of salmon were in. what we got was openings for streams and rivers with reasonably good levels of hatchery input. It would be nice to know what if anything DFO has been able to do to improve it's knowledge base of the health of these streams! Best I know only Region 2 and 3 has these sweeping restrictions. In the case of Reg 3 that was more related to the Big Bar slide.
I think we know many of not most of our local rivers are in dire straits but how much is a general closure helping? The no fishing for salmon rule is very easily circumvented and people in many locations - like the Fraser Bars, continue to do it.