The main reason why HR takes the first round is because:
1. HR should analyze where the candidates match the expected job profile. Have set marks defined for all questions asked and based on the percentage which he/she gets in the HR round, he/she should be forwarded for Technical Round.
2. Should have some verifications with respect to the organizations that he/she has worked.
3. Analyze where the candidate can be an asset or a liability to the organization.
4. Whether he/she matches the monetary budget.
5. Do prior verification to check if the candidate is not a fake.
These various aspects wouldn't be considered by the technical interviewer since their core focus will be technical and work-related responsibilities only. Also, this information has to be checked prior so that only the right candidates are forwarded for further rounds.
!~! BUT I DON'T AGREE TO THIS !~!