In the comments there's a link to consumer rights wiki that includes Raspberry Pi's response to this:
> there may be a minor financial gain in buying a part with say a 2GB part, swapping it for an 8GB part of dubious origin, and reselling it as an 8GB device. However, this brings an element of risk to the user - the board hasn't been tested by us - and is a potential support burden for us, with customers complaining of unreliable devices. We therefore remove the commercial incentive by locking devices to their original RAM size.
> there may be a minor financial gain in buying a part with say a 2GB part, swapping it for an 8GB part of dubious origin, and reselling it as an 8GB device. However, this brings an element of risk to the user - the board hasn't been tested by us - and is a potential support burden for us, with customers complaining of unreliable devices. We therefore remove the commercial incentive by locking devices to their original RAM size.
Frankly, that sounds pretty reasonable to me