I’m still rocking my 2013 MBP, Core i7, 16GB RAM and 512GB SSD. It’s possible to upgrade the SSD but I manage quite nicely with 512GB (with a NAS in the house for mass storage). Unless this machine dies it’s staying for the foreseeable future as it really does everything I need (and then some). At $4k+ to replace it with a similar spec current gen model I just can’t see the value.
My wife is still happy on her 2011 MBA with it’s i5, 8GB RAM and upgraded 512GB SSD. While it stresses the fans out when she’s playing with photos, it’s fast enough for her pretty minimal use these days.
While it’s price that’s stifling the upgrade bug, the reality is that for the last 5 years + computers of all kinds really have gotten fast enough for a large chunk of the market. Unless they fail there is little incentive to upgrade them.