-(으)니까 gives the reason and 만들다 the making, often in the passive 만들어지다 'came to be made': 이러면 슬프니까 만들어진 날입니다, 'it's a day that exists because that would feel sad'. A frequent shape is -다 보니까 만들어지다, 'as things went along this ended up being created' — 돈의 단위가 커지다 보니까 만들어진 돈. -(으)니까 states a reason the speaker treats as self-evident, where -아/어서 would be more neutral.