Regular season is more of an apples to apples comparison across generations.

In the past, the playoffs weren’t as long. The 4th round wasn’t added until 1984. All rounds weren’t best of 7 until 2003.

Plus, the number of playoff games a player plays can vary quite a bit. Even in a championship winning year, the team could play anywhere from 16 to 28 games.

Playoff + Regular season scoring is impressive and maybe you could make the case that it should matter more because it’s accounting for overall mileage, but simply regular season scoring is an easier thing to track and compare in a nice clean number and that’s how almost all career records are kept across sports.