I am currently studying the conservation movement within the UK and I have yet to find the answer as to why places such as the Grace Dieu Priory have been left standing, rather than being completely demolished. Especially as they were destroyed before the conservation movements of the 17th and 18th centuries
In short, the pillaging of ruins for building materials was cut short in the late 18th century by a new appreciation of the past driven by the philosophy of sensation, which valued personal experience and emotion.
The development of the picturesque as an aesthetic category prepared the ground for the Gothic Revival of the 19th century and the creation of the modern preservation movement.