Input APIs for touch, multitouch and gesture were a mess for many years in the browser.
Media queries didn't become a w3c recommendation until 2012 so building a ux that looked pleasant really wasn't possible.
The memory, cpu, GPU, storage and battery constraints were unbelievably tight.
In short mobile hardware and the iOS and Android SDK environments were consumer + developer ready for practically 10 years before the web was ready for mobile.
The real question is how did the web remain relevant while being so far behind this tectonic platform shift?
I think major points that kept the web alive: content addressibility (via urls), ease of connectivity between content (via links), vast amounts of information already in the platform, smoother learning curve for developer technology, and the vast amounts of money/influence Google was willing to put in to keep it's search ads property relevant.