Timing. The core 2 generation was right before we hit a plateau in processors. An i5/i7 macbook from 2014-2015 felt pretty good for 5-6 years, until the m1 came out, and you can coast for another 2-4 years being annoyed some people have a faster machine before they start baking features into the OS that make your machine feel even slower. That’s 7-9 years of use depending on your tolerance for being behind the curve. Mine’s high, so I got 10 years out of it.

Conversely if you bought an i7 macbook in 2019 it would have felt out of date in just 2-4 years, when everyone has an m1 or better and things are starting to slow down from OS changes that expect apple silicon.

If you bought an m1 just a year later in 2020, i’d guess you’re feeling fine 6 years on.