You mean other than the zillion dollars of infrastructure you need to run these systems for a billion users. And the extreme cost to sustain that operation day to day. And the cost to upgrade the infrastructure forever.

Remind me which entities (govt or corporate) are going to subsidize that forever. Remind me which entities are going to front the cost just to scale up.

By that premise - wherein you forget everything other than the first ingredient (the model) - Google has no moat either (got $100 billion dollars lying around?). Nor does Uber (have tens of billions in your bank account to clone their business?).

I'm certain building an app (Uber), or building a search engine (Google), is the super duper hard part.

Slapping a GUI on Linux will kill Windows, any day now.