Why does SpecConstr run far later than specialisation

As far as I understand it, the goals of SpecConstr and specialisation are the same. One works for normal value arguments and one works for special type class dictionary arguments. However, looking at the pass order in `SimplCore`, specialisation runs very early before any major simplification but SpecConstr runs very late right at the end of the pipeline. Does anyone know the justification for this? It seems intuitively that they should work in the same way. Cheers, Matt