I do build apps. This is actually taught as best practice to beginners in many classes. A standard design is pulling everything from a Repository pattern, which

I do build apps. This is actually taught as best practice to beginners in many classes. A standard design is pulling everything from a Repository pattern, which either points to local data or network as needed. This kind of architecture is costly, especially combined with TDD and such needing to cover every possibility on every layer. Adding the repository layer with two data sources is basically 3x tests to write. If time is short (and it always is) adding the repo layer doubles the tests to write/maintain for absolutely no gain. Adding it as needed later isn't so bad, but it's just put off forever. Also, ads don't run if the network is disconnected. Users soon realise that disconnecting is like running ad blockers. Same with some anti-cheat, e.g. changing the time to move forward in idle games.