The Satcharitra mentions 'Salokata' and other types of liberation but then just dismisses them. Why doesn't it explain them in more detail?

You are correct that Chapter 50 mentions and then moves past the concept of the four types of liberation. The text explicitly states, 'The four types of liberation like Salokata—we have no desire for them.' According to the author, this is because the 'supreme attainment' is something else entirely: 'steady devotion to Sai.' The passage in Chapter 50 argues that the very concept of liberation is secondary, posing the question, 'We were never bound in the first place; what connection do we have with liberation?' The primary goal promoted in the text is the 'awakening of devotion to the Saint,' which is said to be the sole means by which the heart becomes pure.