I think this slightly understates the "business development" problems with developing a new OS, and a mobile OS in particular. It turns out that there are certain apps that, if they are not available on your platform, are immediate deal breakers for huge numbers of consumers (to the extent that they will ask for them by name in stores and return devices that won't run them). Often these apps lack web frontends (for non-technical reasons).
Obviously there are technical workarounds that you can attempt but consumers are wary of "knock off" products. So there is a vicious cycle in which people won't produce the content that you need to get users until you already have users. Possibly one can break this by supporting Android apps, but you would have to make the experience as good as an actual android device, which seems both demanding and limiting (because of cross-app interactions via e.g. intents).
In response, Mozilla Research started a "j2me.js" project to try running the WhatsApp J2ME app in JavaScript, sharing some code with the Shumway project to run Flash content. If that worked well enough, maybe WhatsApp would become interested. It did actually kinda work, but the project did not proceed for a number of reasons. Also, j2me.js was renamed "PluotSorbet", due to trademark concerns: