why uniformity is lacking in personal laws

The Hindu Marriage Act of 1955 recognizes customs like the saptapadi, degrees of prohibited relationship (sapinda relation), valid conditions, conditions for divorce, void and voidable marriages etc. The laws on Hindu Women's Property Rights is as under the Hindu Succession Act 1956
The "Muslim Personal Law" is based upon the Sharia (Quran + Sharia). The Muslim Personal Law (Sharia) Application Act was passed in 1937 deals with marriage and succession. (Valid conditions- offer & Acceptance, presence of 2 witnesses, attaining puberty), prohibited relation (affinity or fosterage) But Divorce as per The Dissolution of Muslim Marriages Act, 1939
Christians Indian Christian Marriage Act 1872 and Indian Succession Act
The Special Marriage Act 1954 (marriage for the people of India and all Indian nationals in foreign countries, irrespective of the religion)