Because of a few reasons:
Originally Posted by squirrl
1: AMD put itself into a lot of debt as the result of the ATI purchase.
2: AMD typically targets the low-end, and as a result has very low product-margins.
3: AMD since K8 has typically shipped its products late, which has lead to increased development costs and reduced sales.
4: AMD has been absent from the fast growing mobile-market.
5: AMD in non-competitive with Intel in sales in the Server market.
Shipping lots of low-margin parts is a great way to try and gain market share, but is financial folly. Lets face it: Its CPU side of the house is a mess right now.