It is difficult enough that only huge companies (Microsoft, Google, and Apple), or big open-source projects (Mozilla), have the resources to do it well. Nowada

It is difficult enough that only huge companies (Microsoft, Google, and Apple), or big open-source projects (Mozilla), have the resources to do it well. Nowadays, the browser is handling much of what the OS did a decade or so ago. Email, office productivity, media, games, and more have to run perfectly across multiple platforms (desktop, tablet, mobile). And you can't charge for it anymore. So, yeah, it's an uphill battle