Why don't they sell laptops with no operating system on them in the usa?

When i travelled to korea last year, they were selling some lenovo, acer, samsung, lg, hp, asus, msi laptop models that come with no operating systems and they were like $200-300 cheaper than the window laptops even thought they had almost the same specs.

but here in the us, they always come with the windows unless you buy a macbook or an ubuntu laptop from a weird website. I just want to use linux or something and i don't want to spend a dime for microsoft. I know that i can erase windows and install linux on it but the manufacturers have already paid some money to microsoft when it is installed on your computer at the factory and i don't want to buy any of these products.

why don't they sell any laptops with no os in the us? Is there any law about it?

Laptops often come with quirky strange chipsets and the manufacturer of the laptop sometimes does not support the proper drivers for the operating system "YOU" are interested in installing in it. Now what are you going to do?
I have been installing new operating systems in laptops for aver 20 years and it can be extremely challenging and sometime impossible.
In the last 18 months I have installed Windows 7 Pro in about a dozen laptops when I swapped out the original hard drive for a SSD. Almost all of them were Toshiba. If you get a Toshiba through Tiger Direct "Good Luck" with finding the drivers.
Most of the drivers for laptops can't be automatically pulled in with Windows operating system like on a desktop computer. You got to get those drivers from the people who built them an download them and then properly install them.

Actually there are lots of marketing reasons to have an operating system already installed on a new computer. If you really need a computer with nothing on it, build your own barebones system.

No, there's no law, but there are bulk purchase agreements that give computer vendors a huge discount from the retail price of the operating system. For each laptop that sells with Windows 8 Home Premium, for example, Microsoft might charge the computer vendor $50 (for example - I don't know how deep the discounts go), but it allows them to mark up the price of the laptop by considerably more, because the consumer would have to pay for a retail copy of Windows if they wanted to use it and it didn't come preloaded. In exchange for the significant discount, though, the vendor's contract with Microsoft probably requires them to install Windows on every machine with certain specifications or greater. For most netbooks and some of the cheapest, least powerful laptops, most vendors preload Ubuntu or another Linux variant, but their agreements with Microsoft may not allow them to do that with more powerful machines, and they have no incentive to renegotiate the agreement to allow Linux as an option - and consequently to pay more per copy of Windows sold - because Windows is still considerably more popular among US consumers of higher-end machines than Linux is.