While some religious individuals and groups have indeed adjusted their beliefs to align with scientific discoveries, including the age of the universe, there are creationists who reject or challenge scientific explanations on ideological or theological grounds. The primary reason is that their interpretation of religious texts, such as the Bible, leads them to hold a literal view of creation as described in those texts. They believe that the Earth and the universe were created in a relatively short period of time, typically in line with a literal interpretation of the creation accounts found in religious scriptures.
For such creationists, changing the timespan to accommodate scientific evidence would contradict their deeply held beliefs and undermine the perceived authority and accuracy of their religious texts. They may view scientific explanations as challenging their religious worldview and see the acceptance of an old universe as compromising their faith.
It's important to note that not all religious individuals or groups reject science or the notion of an old universe. Many people find ways to reconcile their religious beliefs with scientific understanding, often by interpreting religious texts symbolically or metaphorically rather than literally. This allows them to appreciate both the religious and scientific aspects of the world without perceiving a conflict between them.