Defenders close in, that puts them on high heels and allows offensive players to attack off the dribble, once you break first line of defense ,rest of a defense normally crumbles and you can either find another open man or finish yourself.
When you watch random kids/people / even pros play 3 v 3 street ball, teams that can't shoot just have situations where even best players look like scrubs because 5 people stand around rim , you can't attack a rim with so many bodies. When people in street ball can shoot, it feels like 1 on 1 game, because other defenders stay out on perimeter, glued to their assigments, and great driver looks like Lebron.
In pro basketball it's even more clear, because you have 9 bodies ( + handler) . If 9 people stand in 15 feet space around rim, i don't care are you Lebron, prime Westbrook, prime Jordan or Hakeem or Shaq, you won't ever score easly because you will have 6 even 8 hands around going for a ball, pushing, shoving, forcing contact, and you will simply have no space to create force for drive.
3 point shooting itself helps you remove people from paint, allowing rest of offense to be easier to unlock.
Nuggets are great example how you don't even need to make those shots, to have better offense with great shooters & ball movment. 5-28 for 3. Won game easly. In fear of Murray, MPjr, KCP, Lakers would overcommit to shooters and exposed themeslfs to like 40 points worth of layups & dunks.
Just a little nugget on fear of movment and spacing. 4 Lakers players don't have eyes on ballhandler nor ball, they are on such high alert of movment that they don't even follow most important part - damn ball.
Because Davis has no clue what's going on, another person can't see sh** behind Jokic, Porter gets wide open dunk on set defense in 4th quater of must win game in playoffs. And Murray's man is taken out of defense because he is chasing Murray 28 feet from rim. He is pretty much usless for team defense if ball isn't in Murray's hands and Murray isn't target on that offensive set.
