Perhaps the author of the fanfiction wanted to give Harry a weakness or something he needed to overcome. It might also be that the magical aspects of the story overshadowed the need for him to learn to swim. Or, it could simply be a random choice by the author to add an element of surprise or novelty.
Maybe it's just never been something he's had the chance to learn. Or it could be part of the plot to create some challenges for him.
It could be that in the fanfiction's specific world or circumstances, there weren't opportunities for Harry to learn swimming. Maybe there was a fear associated with water that prevented him from attempting to learn. Another possibility is that it's used as a character trait to add depth or create unique storylines.
Look to Chapter 23 for the clearest answer. It begins with Although Jiang Li exerted very little strength, Jiang Yan instantly felt..., keeps building through The pain twisted his face grotesquely as he dove headfirst into the sofa., and lands on However, just as she buried herself in the study.
The best chapter pointer here is Chapter 55, "I Can Prove Everything Miss Jiang Said Is True!". It opens with Su Yinwan hadn't expected that, in just one day, Jiang Li's reputation had... and closes on He Yun's fans were immediately displeased..
The best chapter pointer here is Chapter 56, "Popular Host L God Actually Supports Jiang Li?!". It opens with Lei Shen originally had no idea about the trending topics on Weibo. and closes on At this moment, Lu Xingchao was still in the dark..
If you want the clearest chapter reference, go to Chapter 23. Early on, Although Jiang Li exerted very little strength, Jiang Yan instantly felt...; later, the chapter leans on The pain twisted his face grotesquely as he dove headfirst into the sofa..
Chapter 22 is the strongest chapter-level answer because it starts from Hearing this, Su Yinwan looked at Shang Shaojing with a face full of... and follows through on Jiang Li's righteousness temporarily shut Jiang Yan up, but after a few....
The best chapter pointer here is Chapter 19, "I dare you to touch her!". It opens with What criminal law is this or that, this was originally none of your... and closes on Please give me Miss Su's birthdate." Mr..
Chapter 21 is the strongest chapter-level answer because it starts from Jiang Li's clear and logical explanation had everyone stunned in place. and follows through on But the implications could be different..
If you want the clearest chapter reference, go to Chapter 25. Early on, Therefore, from his childhood, Jiang Shixu had felt an extreme aversion to...; later, the chapter leans on Over time, he naturally developed a gap of estrangement between himself....
A practical answer is Chapter 8, because it turns the idea into a concrete scene. The chapter opens with The resentment that had barely calmed among the crowd surged back two..., adds pressure through Why keep harping on the fact that he wasn't a decent man?, and ends on Other people with a.