Why is it ok that apps don’t respond to device orientation but webpages are expected to?

There are plenty of mobile apps that only work in a single orientation. Landscape (Garageband, lots of games), Portrait (Settings, Phone, Remote, App Store, Twitter, Facebook, lots of games)

What justification is there for not allowing web pages to do the same?

It seems like the same rules should apply. If I'm making a game in a webpage I might want to force a certain orientation, same as a game app. If I'm making a mobile web app or a mobile targeted site it seems like I should be able to force an orientation just like native apps do.

Sure, for a content site letting the user choose is fine but not all web pages are content sites.

Take 2048 for example vs Threes! Threes!, being a native app, forces portrait mode. Why shouldn't 2048 be allowed to do the same thing? That example shows why not allowing a web page to force orientation is particularly bad UX. The game becomes unplayable when in landscape on a phone. Sure, for that particular game maybe it could be resigned to reflow but there are plenty of apps and games for which that's not true and if the page reflows could easily ruin the user's experience.

I know 2048 can't because browsers don't allow pages to force orientation. My question is should they? If apps are allowed to why not web pages?