Certainly I bet a lot of 2015 MacBook Pro owners are hanging on for dear life because the device has USB-A ports and HDMI ports, without needing a dock. The lack of USB-C is an issue going forward however.
Still, for those who have to upgrade, USB-C docks are getting down to the £25 price range (when on offer at least) so maybe this is becoming less of an issue for some (and at least they have an advantage of only needing one plug in/out action). And some monitors are getting USB-C DisplayPort input now, although monitors have an even longer replacement cycle in the home.
Soon we might return to where we used to be in the 80s, where a piece of equipment would last 10 years in the living room (TV, stereo) and then another 10 years in a secondary room.
Regarding computers however, surely a huge factor in the lack of upgrades is because Intel have made negligible improvements in 5 years because of their 10nm debacle? Additionally DRAM stalled in capacity over the past few years as well. The only thing that improved was SSD capacity, which
AMD have caught up (and with Renoir this month they will exceed Intel in performance, power consumption and cost in laptops for the first time) and look to have a path to 3nm over the next 3 or 4 years, hence performance will increase greatly over the next few years. And DDR5/LPDDR5 is coming online this year.