Pretty much all of these programs (Glade, wxFormBuilder, etc) have a similar approach, the point is that the way Delphi (and Lazarus) works is with you working directly with the live instances of the objects that will be serialized on disk - there is a 1:1 mapping between all those and the information is extracted directly from the objects themselves.

In a way Delphi is kinda similar to how Unreal Engine works whereas Glade is kinda similar to how the original Quake engine worked.