Heh, tell that to those of us they lied to for 3+ years about first gen mobo support only to backtrack when competition showed up. That credibility they have is weak tea and is very much in doubt.
A lot of people overlooked a claim that AMD was rewriting AGESA to make it universal. A claim I absolutely believe was true. The timing works out. The first AGESA versions would have been written with a limited budget and few developers. In addition, the architecture was brand new. I would even be willing to bet it was ported from previous architectures to save time/money. As new chips came out, it was expanded to support them, at the expense of size. Later on, with a much bigger budget and far more development resources, AMD was able to rewrite it from scratch, which allowed AMD to make smarter design decisions, thus saving space.
This is speculation, of course. However, if you dig through comments, posts, and tweets, some direct from OEMs/ODMs, you will find that the narrative seems to support this.
I will disagree AMD did this to sell new boards. There are other ways to do that.