Why do many novels written by some writers have very similar story patterns?

This is normal. Even real writers, some people started by imitation. For example, there are many imitations in Chen Qingyun's martial arts novels, which can even be regarded as plagiarism. However, Jin Yong is quite tolerant and doesn't care about him.

Moreover, there are still a few people who are not qualified to call themselves writers. This "similarity" is self-evident. There have been many lawsuits. If you want to make money, it's all about money. If you are incapable and unwilling to contribute, you can only copy others'. Euphemistically called reference.