MC didn't fall for him simply because she doesn't like him, and that's okay. It was clear they weren't compatible, and Chanhee knew it. He didn't even try to work on their differences like people in a relationship usually do, which is why his friend called him out.
This!!! I sternly believe that the author/this webtoon had chapters of the FL and Chanhee together was to give answers to what you have thought. We, readers, often pity the second ML, contemplating that he should've been end game. It's true, I did that before coming across the following chapters. Yet, it's amazing that the author included the answer of "what would happen if they DID end up together" and we had the outcome. Additionally, I don't think Chanhee was ready for a relationship seeing how he did in those chapters, and it's completely normal! Sometimes, we get so infatuated and limeranced with someone we like that we forget to act right when we have them (not objectifiying, duh).
this is why men think being a nice guy wont get you a bitch. also about the ML woojin pisses me off, he acts like "IM HURT" and all depressed when he thought she was dating chanhee and then when she told him she likes him he was like "since when? okay". meh.
also, chanhee was like "maybe im not good enough" when he cant make MC fall for him, i feel so bad for him.