The problem is that AMD never had great adoption in the enterprise market. Before dropping out of the performance market, AMD's enterprise offerings were slim. While the Opteron CPUs (x86_64) were considered decent and worth their money at the time, the bigger issues were the motherboard and chipsets. They had a couple of bad server chipset releases and the number of compatible and available motherboards decreased. This maked it hard to find servers that used AMD server CPUs. This lead to poor adoption rates.