The intention was never for you, the person who bought your computer, to be able to pop a new CPU into your Compaq five years later.
Standardized, modular parts were always all about the OEMs, who were all trying to build an industry by cloning the IBM PC. They could have a variety of manufacturers making various components and as long as everybody followed the standards, they could pick and choose parts to create SKUs for various needs and then sell them to you, the end-user.
The fact that a twenty year-old me could spend a summer saving up for the parts to build a brand-new Pentium II computer and then spend an exciting weekend putting it all together was a side effect of all that.
A side effect many of us enjoy, obviously. And a side effect that developed into a small industry of its own, with various companies (even Intel and AMD at times) targeting the "enthusiast builder" community.
When you understand this, though, things like soldered-on memory and CPUs make sense. The reasons why your 1988 Compaq had standardized IDE drives and memory slots are utterly inapplicable to a 2015 MacBook.
I hate the non-hackable place to which PC hardware is headed, but I don't get angry at it.
Almost no other category of consumer good works in the modular way that we nerds wish that everything would. Aside from the fact that they run on the same gasoline you can't put Chevy stuff into a Ford; you can't even put Ford F-150 stuff into a Ford Fusion. Your toaster oven, your ceiling fan, and your lawn mower are the same way.