Because they hit them extremely well. Paul is one of the best midrange shooters ever based on percentages we have (maybe the best) so he’s fine when taking those shots and Kyrie is insanely gifted.
The farther you get from the basket the lower the percentage of a shot going in declines...whether you shoot a 5 footer or a 20 footer the points are the same. Two points. Once you get past 15 feet, the reward is much higher for taking 3’s.
Let’s take aforementioned Chris Paul. Paul. an amazing mid range shooter, is a career 46.2% from 16-3P. Paul, a very good 3P shooter but not elite, is a career 37% from 3. If he takes a 100 shots from not ranges, that’s 111 points from 3 to 92 points from 2. The mid range isn’t worth it. Even if that percentage dropped to 33%, the 3 is still worth it.