Oracle Developer Senior interview questions

4 round online interview First 3 rounds: DS Algo 4th round: System Design questions and concepts. Job description was incorrect, they were expecting system engineers and the description was for java app developer

It was an online assessment. After that first round of interview where there were 3 java questions on screen sharing, few verbal question which went on for an hour. Then 2nd round of interview. Which was again few java questions on screen share and few verbal questions on all technologies i have mentioned in my resume. Both happened on the same day. then a managerial round happened next day, where i was asked my location preferance and salary expectation and i agreed to what they have proposed. But after that HR ghosted me. I dont get the culture of Ghosting, either they can inform us on call or they can drop a formal mail that our candidature is declined. What's with ghosting?