Then why did Apple settle so soon...?
My first guess would be that Qualcomm saw the writing on the wall and concluded that they'd have to give Apple a considerably better deal anyway, just after years and millions of dollars in out-of-pocket litigation costs.
Second guess is that Apple found out that Intel wasn't going to be making 5G modems after all, they announced it something like the day after the Apple-Qualcomm settlement was announced, and that hence the least worst outcome would be achieved by settling before Qualcomm found out.
Either way, for the sake of the whole mobile industry I genuinely hope this judgement survives as intact as possible trough appeals. Qualcomm has for decades been an absolute nightmare to deal with because of it's misuse of FRAND patents that has allowed it to keep competitors without extremely deep pockets out of the market and those with deep pockets from succeeding. The only actual losers in this instance are Qualcomm shareholders.
AMD would love the deal as they are already friends with Apple with their Radeon GPUs, but I doubt that AMD can produce things in volume that can match Apple’s demand. Plus, AMD laptop chips are not as efficient as intel’s in general, and Apple prioritize performance per watt. And if Apple was going to switch, might as well switch to their own chips right away. Apple love vertical integration of their business whenever possible.
Considering the volume AMD is already doing and has done for some time already I genuinely doubt volume is an actual blocker issue for a Mac Pro with an AMD CPU. If anyone's having issues with volume at the moment it's actually Intel because of their failed move to 10nm and just too much of their product catalog relying on the 14nm node.
No, the real reason why Apple hasn't followed many other hardware manufacturers that have recently introduced a slew of AMD-based systems is most probably the additional engineering needed and Apple already being over-stretched in terms of their engineering resources. We can see this fairly clearly in how the Mac Pro has been effectively abandoned, how long it took to get refresh the Mac Mini along with all their other neglected products.
Who knows, maybe the new Mac Pro that's supposed to come out this year will be powered by a Ryzen Threadripper chip? But we do know that with AMD moving to TSMC's 7nm node they'll have the efficiency advantage in the x86 space until Intel finally gets their 10nm process ready for volume production, which isn't going to happen until well into next year at the earliest.