Question

Why did most scientist reject wegeners theory for nearly a half century

Answer 1

He couldn't provide as much satisfactory explaining for the force that pushes or pulls the continents also because it contradicted their ideas about how mountains form.

Answer 2

I think they were also too skeptic to believe the ocean did move or pull apart, even today do you believe that the continents broke from one big flat plate, and that they pulled apart? They also wonder what large force would be responsible for the movement.

It was much later that evidences from plant and animal features that had similarity from two different planets came up that scientists began accepting the idea of continental drift.
And similar rock strata from two different opposite continents, showed similar rock strata.
All these evidences came up much later after Alfred Wengener.

So Alfred Wengener was honored Posthumously.