To me it's really that Wordpress developers / community are not taking mobile seriously. Poorly mobile optimized themes are just a symptom of the problem.

The consequence is a generation of Mobile developers are ignoring Wordpress, at least in their apps. Wordpress needs to have a drop-in SDK that allows content from an app developers blog to be displayed in a friendly way in-app, plus push notifications / badges etc. to inform users of new content. How do you tell users about new features in your app for example?

Then there are some deeper questions to answer like blog comments - do they make sense on mobile at all? Most people aren't going to write more than a sentence on their phone. What about finding different ways to provide feedback? Yelp for example spend a long time soul-searching about whether to allow reviews from mobile - http://officialblog.yelp.com/2013/08/oh-snap-yelp-app-now-po... - I don't think they found the answer but they certainly saw the problem. But that's another story...

100% poorly designed themes, WordPress does just fine on mobile and all of my websites pass Google's mobile testing tool which, is enough for me (and they look great.)

I do admit that there are probably way more bad themes out there than good, and that most WP 'developers' do not stick to the codex / standards and just want to make money on themes.