Why did medieval monks disapprove of decorative churches?
Decorative Churches were almost entirely Catholic or Anglican or similar ideologies, and in Protestant countries the Pope and his influence was almost universally despised. A widespread fear in these counries was of one day being ruled by the Pope and so people reacted at a local and national level against Catholicism (and Anglicanism which is similar). Therefore one of the reactions was disapproval and destruction of churches, rituals (the Mass etc.), idols etc. that seemed to celebrate the Pope and Catholicism. The reason that decorative churches were assumed with Catholicism is because Catholics didn’t believe in pre-destination (i.e. they believed what they did in their lives would mean they would or wouldn’t get into heaven) and so would often make donations to the church to try and “buy” their way into heaven, hench the lavishly decorated churches.