There is almost no maintenance work for bespoke apps apart from infrequent updates to keep OS and hardware compatibility as the environment slowly changes.
Keep in mind, these are not products in the endless feature treadmill promoted by scrum.
I don't particularly doubt your experience. But if you have struggled to maintain an app that is effectively complete upon inception, it means that changes in your environment are so common that it's a surprise you get anything at all done.
Keep in mind, these are not products in the endless feature treadmill promoted by scrum.