To elaborate on that:
An OEM would be really stupid to bundle a version of Windows that hasn’t been on general release to the public for an amount of time for exactly that reason – give time for showstopper bugs to be found.
An OEM would be really stupid to bundle of Windows that hadn’t been extensively tested on their own hardware, and that takes time. Sure, they’ll get the builds early, but still.
To change their software loadout would involve updating their master images, which takes time.
Why would they want to do that anyway? It labour-intensive and gains them nothing. Every OEM system I’ve ever set up – and that’s a LOT – the first thing it does is spend half a day doing Windows updates.