Yep, I think this is it. I also have 5 years old MBP with the original charger, and it's still fine. I'm not a very careful person, and in general never wrap cables in loops, just cram them in the bag. Sometimes my cables get impressively tangled, but I think I'm still actually saving time by skipping the meticulous wrapping every time I take off (at least twice per day).

So maybe if you stop taking "good care" of your charger, and stop wrapping it in a tight loop, it will actually last longer.

That said, a lot of people seem think you're supposed to wrap the cables. After all, the MBP charger has built-in hooks for exactly that purpose. The charger is badly designed if wrapping the cable around the provided hooks causes it fray very quickly.