Does Apple actually invests into laptop/desktop development? They are usually couple of years behind competition (DDR3, Sky Lake chips). While their ARM chips are heavily developed.
I think they decided long time ago that ARM is good enough, and are waiting for train to stop to change the engine. It is not about Intel quality, but about saving money and independence. AMD is not even considered as an alternative...
I do think they actually invest significantly into laptop/desktop development. If you look at the teardowns at iFixit, they are pieces engineering art. No other manufacturer offers that nicely designed devices. Just think of the new Mac Pro having no internal cabeling, everything, including the extra power supply for the graphics cards, is on the motherboard.
But of course, one can (and I do) disagree with some of their design choices, like non-exchangeable SSD and using far too much glue in the designs.
LDDR3 was used for power efficiency. Apple generally only updates to newer generation CPUs when (a) Intel can supply enough and (b) there's a significant performance or power efficiency improvement. As far as I can tell they make the decisions on engineering grounds.
People seem to be buying them anyway. If we consider Form over function could also be playing a role here, Apple's obsession with making their notebooks thinner ditching intel will help a lot with that cause they can at least keep the same battery life with a smaller battery.
I think they decided long time ago that ARM is good enough, and are waiting for train to stop to change the engine. It is not about Intel quality, but about saving money and independence. AMD is not even considered as an alternative...