First, I’ve been to Astoria Oregon, and I assure you that people live there. It’s not Vancouver, but it’s a legit town.

But I get your question. I think the answers are complex and technical, but my understanding is that people migrate and settle, and then population centers often grow based on a mix of natural features and where human-made resources like centers of education are constructed. So it’s really more of a question of why were the locations of Portland and Seattle better.

I’m not a geographer, so I don’t know the precise features, but my guess is that Portland and Seattle were located in areas that offered most of the benefits of this coastal region in terms of access to the ocean but had greater benefits and fewer downsides. I’m just speculating here, but my first guess would be that the weather inland is less intense. It might also provide better access to freshwater and arable land.

But people do live there. And if you live in Newport or Lincoln City you’re two hours from an international airport. That’s not exactly undeveloped wilderness. People just chose to settle a bit more inland along bays, which considering how rough the weather in the coastal Pacific northwest can be, seems sensible.