Mac computers are expensive, particularly outside of the US. If an older Mac is still functioning well, why replace it?
Also, the Macs, especially during the Steve Jobs era, and before the introduction of the butterfly keyboard + touchbar Macs, were built like tanks and worked very reliably. Hence, many people still keep using the older Macs; they were just superior products before Apple got influenced by the iPhone design and build aesthetic and brought it over to the Mac, with disastrous results.
Also, the Macs, especially during the Steve Jobs era, and before the introduction of the butterfly keyboard + touchbar Macs, were built like tanks and worked very reliably. Hence, many people still keep using the older Macs; they were just superior products before Apple got influenced by the iPhone design and build aesthetic and brought it over to the Mac, with disastrous results.