There's certainly an appeal to specific formats like 70mm, but that comes along fairly rarely. I haven't been to Portland, but I have seen 70mm films in classic theaters. They're rarely comfortable, the sound usually sucks, and the lack of stadium seating can be brutal, but you're there for the insane effort that went into end-to-end 70mm production.

Of course, I saw Dunkirk in IMAX 70mm projection at the Metreon in San Francisco, which is a state of the art screening room, but that will probably only ever happen every few years. Sadly the Metreon recently remodeled with completely terrible seats (only in the IMAX room), so I'm rarely tempted to go there.

Seats in the IMAX room is indeed very bad. It’s sad because the screen is 2nd largest in North America. But your only memory of the movie becomes how much pain your back and behind are. Try the shoreline cinemark in MV, very comfy seats!

The Metreon IMAX is such a shame. They installed that incredible new digital projector (Dolby laser, I believe) but at the same time ruined the seats.

There's definitely Cinemark theaters with 70mm. I saw Dunkirk at one.

More importantly, though, not very many movies were/are shot in that format. Not enough to really build a business on.

70mm film?

A number of Cinemark theaters that featured Dunkirk in 70mm listed here: http://www.slashfilm.com/dunkirk-70mm-locations/

There's nothing stopping one from going to a special theatre for that one film shot in 70mm. But most movies are not that.

You are ignoring all the other arguments. Better movies, better food, a general lack of children.