Why is manufacturing expensive in developed countries?

Infrastructure and technology may make manufacturing easier, but developed countries have much higher costs because of other costs: the real estate of the factories costs more, disposal of hazardous waste costs more, and employees cost much, much more. The cost of living in general is higher, and factory workers must be paid a living wage. Many factories have workers' unions that negotiate contracts for pay and benefits as a group. Unfortunately, by insisting on high wages and benefits of all kinds, businesses don't find it worth their while to bother employing these workers, so they move their manufacturing overseas. Unions have negotiated their workers right out of jobs in many cases. Even in right-to-work states (no unions), it still costs more to employ workers than it does to use third-world countries and pay to ship the goods halfway around the world.

Partially labour costs, partially higher standards in occupational health/safety . You can't legally run a sweatshop with slave-like conditions in the developed world, and no one would accept a job for 1-2 dollars a day either.

High end manufacturing does have potential in the developed world, but they create high-end products. If you want cheap plastic crap or cheap textiles, you have to outsource to places where labour is close to free.

Labor Costs are the biggest expense and infrastructure does not affect that.