Why Do Cultivation Protagonists Suck?

[Zirrboy]

You miss a point though. In a strength based society everyone else is enemy. It is not a 1vs1 battle between sects. If you fight against another sect, others will fish in muddy waters. So even if you are the son of the current clan leader. You can't just kill disciples of other sects for face.
Remember these sect are old. They already have many enemies and allies. So anyone who adds more enemies without a reason or humiliates allies would be put down.
So, in a strength based society, even fights between 3 year olds can escalate blood feuds easily. That's what there are usually code of honors that shows what you can do or can't. Usually you can't do anything to anyone unless your leaders considers them as enemies.
They would kick their own young lord's *SS or kill him even instead of adding more enemies or losing a long lasting ally. So that usually the leaders are polygamous and have many children, one son is often not important enough to gain an enemy or lose an ally. Especially if he is an unruly one.

While certainly true, this also applies to the victim.
Would they risk being picked off after a grinding fight against the aggressor's sect for the sake of an unimportant disciple?

Of course they have face to lose. But inciting fear in people with excessive reaction does not just make them respect you, but could also unite them for the sake of culling you.
But I'd say in the end tolerance and restraint balance out in proportion to their powers.

And for someone unaffiliated, like most MCs, none of this applies in the first place.

 

[SakeVision]

lack of originality and pandering to tropes, as well as being paid for chapter/word count leads people to create unoriginal stories that are set for quantity over quality

 

[vaurwyn]

It is because most cultivation stories are power fantasy, and low quality ones. That means the MC is allowed to act without any consequences, he is above the rules that he enforces for everyone else.

This genre works because it is appealing to our baser instincts. Think of when someone who annoyed you so much you wanted to punch him. We don't do it in reality because we have self-control and know it would be overreacting, but we have no such limits in books. The whole face slapping genre is basically built on the pleasure we get from petty revenge.
Even when the Author says the MC is actually a bad guy, he will only fight even eviler guys, because we don't want to disgust the audience.
Secondly, character writing in general is hard. It takes time and effort, and in a system where you are paid for quantity over quality, it is often not worth it.
Entire books have been written to explore moral conundrum, but that is not what most Xianxia novels are about. They only care about the next big fight, and don't take it to heart. This makes the characterisation very superficial, and it is very easily contradicted by accident.

Now since we are on this topic, I would like to do a bit of self promotion. I started a book with the main goal of exploring a cultivation inspired magic system, because like you, I found they often lacked proper characterization and worldbuilding.
A lonely exploration of Tao
The MC is a normal human, slightly weak-willed but with clear moral values.
Be warned, the story gets quite dark, with the MC falling into depression. He gets over it, but maybe that is not your thing.

That might be another reason for the lack of morals in other Xianxia. Most of these novels have lighthearted tunes while simultaneously depicting horrors worse than WW2. The disconnect makes it hard to realize "Oh no my MC is also doing something absolutely horrible."