Because Jaylen makes a lot of bad basketball decisions, for someone so smart, he does not have a good basketball IQ.
Ya I don't really think he makes any worse or more numerous mistakes than Terry, Tatum, Morris or really any one else on this team for that matter. I actually like his basketball IQ, he takes far fewer bad shots than most of his teammates. He Has a very low turnover percentage, his shots profile (mostly threes and at rim) is good, he fouls less than he used too, he is one of our three best defenders. He's not a good passer but even that has gotten better this year. So I'm not sure what people reference when they say he has a low basketball IQ, to be he usually makes the right play. He des make mistakes, but so does pretty much every player on a rookie contract.
To the OP"s point I think he gets yelled at a lot because A) Considerably more is expected of him on the defensive end than Tatum, Rozier, ect. He is a better defender than those guys, more natural talent in that area, and so the guys on the team expect him to be good at it and get on him when he messes it. Its the old "tough love" approach. In this way I dont think its a bad thing. B) He's a young guy. Hayward is not gonna generally get yelled at, he's a vet coming back from injury. Kyrie was awful for all of February on defense and didn't get yelled at, he's a star. Morris is a vet who other vets wont call out, as is Smart and Horford (and they dont make many mistakes anyway). The point is vets dont generally ride on other vets, young guys C) Personality. Jaylen is quite guy, the quiet guy is naturally gonna get yelled at more by the loud and annoying guys (like Smart and Morris), doesn't mean its right or fair, Morris for example messes up more on defense than anybody but Jaylen isn't gonna yell at him, he's not a yeller.