Tech Mahindra Software Engineer interview questions

It was a walk in drive , first round was technical which was kind of easy with only basic of core SAP and little bit of OOPS concept , I cleared it and was told that second round would be an aptitude test by next three four days as I have less than 40 months in experience , but instead suddenly I got a call from them that they have arranged a client interview and I have to clear it as well , later I cleared both client interview and aptitude exam , I was told that I will get a call from hr for further process but its been weeks and I am still waiting. Can't understand if they don't have opening why waste time of candidates , and why so many rounds instead of saying no. It's frustrating.