The main factors could be that the anime team wanted to add their own twist or they had to make cuts for better pacing on screen. Sometimes, licensing and production issues can also play a role in deviations from the manga.
It could be due to various reasons like creative decisions, time constraints, or the need to adapt for a different medium.
The Promised Neverland anime not following the manga exactly might be because they wanted to reach a wider audience or because certain elements from the manga were difficult to translate visually without significant changes.
The best chapter pointer here is Chapter 48, "All the Bitter Teas Have Been Taken Away". It opens with He Yun felt guilty for initially ignoring Jiang Li on purpose, and with... and closes on Besides, everyone's phones will be replaced with special smartphones....
Look to Chapter 18 for the clearest answer. It begins with In the corner, a girl in a black dress sat quietly, holding a glass of..., keeps building through Her serene yet cold temperament, along with her exquisitely beautiful..., and lands on Hurry home, what is a young lady like you doing.
If you want the clearest chapter reference, go to Chapter 52. Early on, The village chief and the woman behind him exchanged a glance, "This...; later, the chapter leans on might not be a good idea, you guys are still filming, we don't want to....
The best chapter pointer here is Chapter 65, "Jiang Li Missing?!". It opens with Several minutes later, the room remained silent. and closes on What's the deal with these two?.
The best chapter pointer here is Chapter 63, "Far Exceeded Expectations!". It opens with During those seven days, he thought he had completely escaped from that... and closes on It was already past midnight, but the conference room at Xingmei....
The best chapter pointer here is Chapter 33, "Variety Show of Villains". It opens with Following the announcement, five artists respectively reposted the Weibo—... and closes on Although Su Yinwan was considered half a goddess to him, the whole thing....
A practical answer is Chapter 54, because it turns the idea into a concrete scene. The chapter opens with Five minutes later, the people of Chixia Village, who had received the..., adds pressure through Even the trolls in Jiang Li's live stream room were not very active..., and ends on She was.
If you want the clearest chapter reference, go to Chapter 64. Early on, Chixia Village lay in tranquil slumber.; later, the chapter leans on Gray clouds embraced the green mountain mist, shrouded in a gauzy blur,.... By the close, He'd been a host for so many years;
If you want the clearest chapter reference, go to Chapter 14. Early on, Lin Manru had a rare good night's sleep.; later, the chapter leans on After freshening up, she specifically went to Jiang Yan's room on the....
A practical answer is Chapter 24, because it turns the idea into a concrete scene. The chapter opens with Not only that, even the non-mainstream photos she had previously posted on..., adds pressure through Just because of his arrival, both were severely affected by public..., and ends on Shi Xu.