To pull from Folding Ideas:

Vatican II is in some regards progressive, but only as progressive as needed to retain membership and improve political relations with other conservative organizations.

This is basically the modus operandi of not just Vatican II, but of most policy changes the church makes. Modernizing, reforming, and liberalizing are reactive steps they take to stem the loss of parishioners and thus mindshare in society.

… in other words, with external pressures, individuals and organizations may behave better not because of their inherent beliefs, but because of considerations of social expediency and enlightened self-interest. Buchanan differentiates between improvements from a moral point of view, which are caused by external factors, some possibly independent of human motivation and agency, and genuine moral progress.