Why did the Church make Opus Dei a personal prelature?

Personal prelatures are ecclesiastical jurisdictions provided for by the Second Vatican Council and the Code of Canon Law that are created to meet specific pastoral needs which require greater flexibility. Opus Dei combines in a single worldwide institution priests and laity, women and men, sharing the same vocation of spreading the ideal of holiness in the world and the sanctification of work. Being a personal prelature, however, "provides Opus Dei with an ecclesial configuration fully in keeping with its foundational charisma and sociological structure" (the Holy See's 1982 "Declaration on Opus Dei").