The thing is that mobile browsers fill fight you tooth and nail against providing a good experience to your users. There is the obvious stuff like lots of API not being available, but the bigger issue to me is how many common convenient UI patterns that users accustomed to native apps expect are really painful if not impossible to provide, e.g. there is no reliable way to react to the keyboard opening, or how scrolling will expand and shrink the browser UI. CSS Houdini being abandoned also makes it really hard to properly do really custom UI. I really wish there was platform with the distribution and security model of the web that was designed for apps from the ground up.