What's the model for integration and maintenance in that case, then? Just re-create the app every time?

I think the journey means different things to different people. Not everyone is interesting in building their own power generation plant, mining silica and forging their own chips, writing a programming language from binary. I’d love to do that stuff if I didn’t have bills to pay, but sure am quite glad to skip through the knarley JavaScript implementation details and focus on the parts I know well (backend, data modeling, translating domain specific knowledge into product) and get something to market.