It didn't "get lost". Microsoft deliberately obscured it.

[Microsoft] “testified that a free restore CD was worth the same price as a new Windows operating system with a license. … This was false and inaccurate testimony provided by Microsoft in an attempt to set a precedent that will scare away future recyclers and refurbishers from reusing computers without first paying Microsoft again for another license. … Anyone successfully extending the life cycle of computers or diverting these computers from landfills for reuse in society is essentially standing in the way of Microsoft’s profits.”