The reason that most danish churches look the same, is because they where build the same. When christianity first became a thing in Denmark churches where at first build in wood, but latter craftmen was imported from Germany, France and the Netherlands to build stone churches. Most of these churches where build in small communities and followed a very spartanic roman tradition where you only had a nave(kirkeskibet) and a choir(kirkekor) and that was it. There where no tower and even transepts where only used in the cathedrals. The churches where chalked to protect them from hard weather. We assume that white was used simply because it was the cheapest.

Now the earliest churches would be build with stones and properly have had a wooden roof, but with when the knowledge of making bricks came to Denmark in the 12th century many churches was given a brick roof and they are red, simply because that is what was cheapest.

With the knowledge about how to use bricks many churches in Denmark started to be build with bricks, because big stone are really rare in Denmark. This enabled the builder to make the churches taller and slender, properly inspired by the gothic style, but they continued to be build with just a nave and an alter. Around the 15th century the majority of the danish churches had already been build and when new i spiration came to Denmark from the southern countries, instead of building a new church people either ignored it or rebuild a bit on the old church.

So many danish churches started looking practical the same, but have changed over time depending on how the perish wanted to upgrade their church. Some of the most common changes would be a church porch(våbenhus) that would most often have been added in the 14th or 15th century or a churche tower that would most often have been added in the 15th or 16th century.

That is basicly what make up a tradional danish church like this, this and this