It's true that building an MVP is a lot easier than creating a polished product that would scale to tons of users. I would even say that the skill set needed for the two are significantly different. Somebody trained at quick prototyping of full stack app may not have the skills to scale it for thousands of concurrent users and vice versa. But isn't that the reason behind raising funds? If the product demand is proven, funds can be raised to polish and scale the product out.