Why was the most important of Jesus miracle the raising of the dead in Luke not written in other Gospels?

It must be understood that there is no requirement for anything in particular to be recorded in any of the Gospels. Some events are recorded in all four and others in only one. It is also a difficult judgment to make that something is 'the most important of Jesus' miracles.' It is uncertain what criteria one would use to decide this.

The leaving out of any particular event or detail does not imply anything about either the historicity of that event or suggest a contradiction between another gospel which includes it.

There could be all kinds of reasons why one particular thing in Luke is not included in the others. Luke, being a physician himself, certainly was interested in things relating to medicine and healing. This may have explained why he included a particular account left out of the others.

In any case without the details of the particular miracle in question, it is difficult to make only these general observations.