Castles were going out of fashion by the end of the fifteenth century. Advances in artillery meant that they were no longer suitable for defensive purposes. Building, instead of being primarily defensive, changed to a greater concentration on domestic comfort. Although “licences to crenellate" were still granted, they were rarer than formerly.
The main area where castles were still important was in the Debatable Lands around the Anglo-Scottish borders, where defence was needed less from an invading army, and more from the clan from the next valley on a cattle-rustling expedition. The pele houses and border towers are reminders of this.