On the contrary, I think a lot of people believe that localised elimination is possible and, in fact, achievable. One of the ways to preserve this is to keep borders closed. I read what's been announced in WA and it doesn't make me think "what happens
when WA opens their borders?" It makes me think
if WA will open their borders in the foreseeable future.
Allowing pubs, cafes and restaurants to conform to a 2sqm rule instead of a 4sqm rule means that many, many more will be economically viable and their businesses will be saved. But as
@lovetravellingoz points out, that suggests that they believe they will be living without the virus, rather than with it. That's inconsistent with opening up travel to areas with known community transmission.
I expect people much smarter than me in WA have done the cost-benefit analysis of those two scenarios. So far everything seems to me to be internally consistent with a scenario that keeps the WA state borders closed for longer.