Mark McGowan's popularity is at something like 78%, the Liberals were wiped out last election, and I think this is the reason he's being targeted so much by right wing media / liberal premiers, when his message and comments are being deliberately distorted, and they're doing the same with the Doherty institute plans, cherry picking the positive without being clear on the caveats they've laid out too.
Should also bear in mind, WA's economy is dependent on resources and farming, the kind of lock downs NSW and Victoria are seeing would be extremely harmful, keeping borders controlled (not shut!) will protect the most vulnerable and keeps WA businesses going. Our geography is so different to elsewhere, there are single farms bigger than countries here, and there's just a more isolationist outlook due to distances so get anywhere.
Opening up borders is more beneficial for the more privileged, there's a far higher % of population who don't leave the State in normal times. Compared to the East Coast, travel is more expensive and time consuming. WA also has a history of being more independent than the other states, the one and only referendum on seceding from was successful, but was ruled invalid, WA has never implemented daylight savings to keep in sync with the others, so there's definitely a perception that WA can go it's own way to some extent, although I think there's now a feeling that it's inevitable it will get here (my company is beefing up it's contingency plans / workforce plans for ensuring we can still operate our offshore facilities on skeleton staff if need be) but we want to buy as much time as possible. I'd take schools being kept fully open, community sports for my kids continuing, no day to day restrictions over open borders any day for now.