Why does there tend to be more call and response in Sephardi communal prayer in comparison with Ashkenazi minyanim e.g. saying pesukei d'zimra in unison. Also, during the repetition of the shemoneh esreh some Sephardim have the custom of repeating words along with the shliach tzibbur or adding extra 'call and response' phrases to kaddish.

What is the reason for doing this and from where did this develop?