I don't really mean "security through difficulty", I mean that on phones we have sandboxing, permissions, and a bunch of other factors that make phones much mor

I don't really mean "security through difficulty", I mean that on phones we have sandboxing, permissions, and a bunch of other factors that make phones much more secure than the average desktop/laptop. Browsers do provide a pretty good option here, but that comes at the cost of the browsers themselves being highly complex, and privileged software on the devices. OP writing this prototype as a web app would likely have been the path of least resistance to having something work on mobile.