They have reasons for falling in love with the MC, and it takes them time to realize that they are in love. You know, like actual people.

Although I read only c38, I can imagine many girls will flock to him due to (un) lucky encounter, and he'd reject them all to avoid troubles. I've read this similar plot in several other novels and I'm pretty sure where it'd be heading next. The MC would either end up with no romance for rest of story, or there'd be at least one drugged reverse-r*pe...

He lived a normal life on Earth, however he suddenly got a lethal disease that neither he nor his family was prepared for. He died young while suffering from the unknown. So he decided in his current life, that he would live a long and healthy life free of worries, which is why his daoist name he choose for himself "Changshou" apparently means 'Long life'

The MCs junior sister under the same master: She is very clingy with him, but it is understandable given that he practically raised her into her current state. The master was always in seclusion, so he taught her his principles (in hopes that she wouldnt implicate him in any problems), when she was brought in at a young age. Despite his philosophy, he spoilers her quite often, and she is the only one aware from the beginning that he is holding back/hiding.
A junior sister of similar age: She is the top disciple of their current generation. She has the highest cultivation amongst them, and can fight opponents several levels higher than her. She seems like a cold person on the outside, but is in fact very kind to those close to her. After MC saved her life twice when they journey together, she wanted thank him for his kindness. This in turn gets her involved with the MC as she gets very defensive of him. Of course, as of now, the MC thinks of her as "toxic" as she involves him with situations he originally had no intention of getting involved with.
His Martial Aunt: She is the youngest disciple of the top daoist in MCs sect. Though, despite calling her the youngest she is over 900 years old... She is a bit of a tom boy and rather immature, but she is one of the top cultivators in the sect (all the top members of the sect are immortals). Through a a mix of confusion caused by her senior brother and sister, and a complete misunderstanding during a conversation with the MC, she feels attraction toward the MC. They hang out a lot normally, though its mostly the MC asking her for help in exchange for some of his brewed wine (she loves drinking).

Basically, author wrote that protagonist made detailed plans and considered almost all possibilities for enemy reaction. But enemy used the most obvious strategy that they had also tried to use previously (which the protagonist had dealt with previously), and all the important enemies successfully escaped and joined the bigger enemy, and the protagonist went "oh, I didn't consider that possibility" even though that was the most obvious. Now remember that the author tries to portray the protagonist as an extra cautious person who always thinks 10 steps ahead and everybody in that world considers him the greatest strategist ever. And the most infuriating thing is that author writes this as if the enemy did something completely unexpected that the protagonist could never have anticipated, so it's not his fault. Everyone still congratulated him for his "brilliant" strategy.

Also, the protagonist has a powerful attack that can easily decimate large groups of enemies. He has used it multiple times before so his enemies all know about it. But they still attacked without preparing any counter measures. And in this battle where that attack could have easily wiped out a large part of the enemy's forces, the protagonist doesn't use that attack at all without giving any reason why. A lot of his allied forces died in that battle and he just sighed helplessly. He even let his main target enemy get away without major injuries when in the previous battle he had managed to severely injure that same enemy with that attack.

It's like for the sake of plot progression, the author conveniently forgot he had that attack or that his enemies had used the same strategy before.

The author explained that the primordial world was similar to Chinese mythology because someone who transmigrated from China was responsible for developing the world in that way. But that doesn't explain how characters who had nothing to do with the transmigrated person also had the same names as in Chinese mythology etc.