Questions starting with why that involve human factors (in your case, you're specifically asking why people in a company don't do a particular thing) are off-topic pretty much across the entire SE network.
The reason is that they tend to be very open-ended and don't have any particular right or wrong answer. The best people can do is cite rumors or articles that might quote speculation by industry insiders.
And even if you could get a perfect quote from the CEO of AMD stating explicitly the answer to your question in a very recent post on amd.com (to be sure it's 100% authoritative) and had a link and everything, it'd still be off-topic, because your question boils down to a person or entity making a decision to do something, not technology.
So your question would be on-topic (in theory) on a hypothetical but non-existent "Human Factors Stack Exchange" or something, but Super User is a technology site, and your question isn't about technology.
In fact, most questions starting with "why" are probably off-topic for Super User, unless the answer can be made precise, objective, supported by evidence, and completely unrelated to behaviors or decisions of human beings.
"Why can't 64-bit binaries run on a 32-bit Windows OS?" might be okay, since you're asking something that can be answered with a technical exposition. This is just an example, but it might not even be a really good one.
But in your case, there is no way we can interpret your question that would lead us to talking about technology -- every valid interpretation of your question boils down to people and the decisions they do or don't make and the reasons for them doing what they do. Super User is not a sociology site.