Windows 10 What is the difference between Windows OEM key and Retail key? Why is OEM key so cheap?

An OEM license is only good for a single system meaning it's tied to the motherboard. A retail license can be transferred to a new system (still only good on a single system at a time)
back in the day Microsoft would allow motherboard makers to adjust Windows in order to load 'best' drivers for the parts actually installed instead of the default drivers ... so Asus boards had good network drivers and HP had their drivers included on the actual disc that did the Windows install

now day Microsoft takes over your system and loads their own drivers unless you understand how to block that from happening... so if you buy a OEM licence from an actual shop its normally a good way to save a few $ and Microsoft will just replace the drivers anyway

don't buy an OEM from a garage sale