You have to understand 2 things about the NBA.

1. You have to have 1 thing that you are elite at. Not good, elite. SL was elite at penetrating and getting/hitting a 2pt jumper.

2. The NBA is a collection of 25-40 insane level basketball players with multiple elite skills and 420 supporting role players with one elite skill.

SL played his last 7 years at Golden State with Steph and Klay....two of the greatest 3pt shooters ever to play the game. SL's role was to penetrate and A) hit a 2pt shot if he was open and B) penetrate and draw Steph or Klay's man to help side defense so he could then kick to them to hit an open 3. If SL was taking 3's himself at a mid level .350% over the 2 guys shooting 3's at a.430% then he would have been on the bench in favor of someone who understood and played their role.

The NBA is a game of measurements, math, and skill and the players have to have and understand the role of all 3. So I get that the stat on it's face seems outlandish for a shooting guard who played a decade and a half in the league, but it's actually a testament to how good of a role player he was for his organizations.