Planned obsolescence: It's the American way.
Create machines, make them a vital part of your daily life, then force you to continually upgrade a perfectly good piece of equipment in order for it to continue to function by not releasing versions of new software compatible with old equipment.
The Macbook is a well-made computer. I take care of my things, so mine (mid-2012) is in good shape. There is no reason to replace it, other than the fact that the processor won't support newer versions of OSX and the associated apps.
I guess Macs are made for people who would rather poison the planet and further exploit child labour to have the latest thing. Oh, well.