Why do HR or Recruiting Team in Interviewing candidates making them under invistigation instead of giving opportunity to start work with good salary?

Its different, and its not all the time. to get out all of the candidate you should apply Iceberg theory, as interviewers prepare themselves for interview, candidates as well try to search and make themselves the best Job seekers in the globe

In addition, Good Salary and positive interviews are common, but also negative attitude candidates are everywhere we you have to make investigation and discover their Icebergs, also using behavioral attitude question will help 

 it's different from recruiter to other one , every recruiter can chose the way to drive interview not always like investigation as you said  .