Why is it that people clear all the written tests, technical interviews but not the HR interviews in a company's recruitment process even if he/she has technical knowledge?

One reason could be that the person lacks the necessary soft skills or interpersonal abilities that are important for fitting into the company culture. Another reason could be that they struggle to effectively communicate their technical knowledge in a way that non-technical interviewers can understand and appreciate.

There are a few reasons why someone might excel in written tests and technical interviews but struggle in HR interviews. One reason could be that the person lacks the necessary soft skills or interpersonal abilities that are important for fitting into the company culture. Another reason could be that they struggle to effectively communicate their technical knowledge in a way that non-technical interviewers can understand and appreciate. Additionally, nerves or lack of preparation for HR-specific questions could also play a role. It's important for candidates to prepare for all aspects of the interview process, including the HR interview, in order to present themselves in the best possible light.