What do HRs really do ? Does ATS do all ghosting?

I've been actively applying for jobs for over three months, submitting more than 500 applications and cold emails. I’ve crafted engaging introductions, set up both virtual and in-person interviews, yet I’m still struggling to receive a job offer. I wonder if companies or recruiters typically keep 3-4 candidates in mind, extend offers to all, and then make a decision. I’m feeling frustrated by the lack of offers. Currently, I’m in a mid-level role with around six years of experience as a data coordinator. I've successfully converted 15 HR calls into the next round, participated in 12 in-person and virtual interviews, and advanced to five final rounds, but still no offer has come through. I’d appreciate any insights from the community.

I always explain projects with problems solving methodology and what are results of it in concise manner in interviews.

Also for 300+ applications and only 15 calls seems very low . I tailor my resume to application specific and how really does ATS work ? Does it filter 1000 resumes and give you only few 20-30 resumes and you just read 2 lines from the resume and attempt to set up an interview. I really want to understand how things work on the other end .

Asked for feedback but received no response or said moving with other candidates.

Edit 1 this for job market in [USA Canada]