First, look at a map. SF has Vancouver WA across the river. Portland itself can also expand more easily. SF is a Peninsula and so it's much harder to expand around the place.
Secondly, Silicon Valley is a well known global hotspot for IT. Everything else is miles behind. The pressure of all that money in the Bay Area is huge. It's worth noting that these problems were not nearly as bad during the 1980s or 1990s boom. It's only been after multiple booms that the SF real estate market broke. Portland isn't as likely to have multiple booms to the same degree.
Portland and Austin are certainly seeing the price of real estate going up substantially. But surely it's a sign of success and is largely a good thing, unlike the super pricey real estate of SF or Sydney of Melbourne AU, NYC or London.