In some cases because it is easier to say that then admit ignorance. How many Christians would answer that way if asked why church is on Sunday? (Although I am sure there are a good number who would answer because the Bible tell us to.) So, here it would be proper to say: “We’ve always had church on Sunday because the church early on chose Sunday as the chief day of worship as the day Christ rose.” Here tradition was shaped by God’s word, though it was in no way commanded by God.
In some cases it is because people want to maintain a sense of control. Or to please someone. Such as: “We’ve always done it that way,” with the unspoken reason kept off the table: “Because when pastor or so and so suggested changing it then so and so threatened to leave and we did not want to lose so and so’s offering.” Or a tradition is implemented because so and so threatened to leave if said tradition was not implemented.
In some cases traditions have come among Lutherans because of the influence of other denominations, though that does not necessarily make them bad. In some cases traditions arise because of bad theology such as: “We’ve never had communion every week because that would make it less special.”
So, as to how to change this where traditions are harmful to faith? Sound teaching and preaching done patiently. Only God’s word can tear down sinful traditions. Only God’s word can shape edifying traditions in the church.
Pastor Gary Hall
PS For some interesting reading, check out p.13 and following of this issue of Logia magazine: http://www.logia.org/fullpdf/2003124.pdf