Really strange... This kind of problem may happen on other systems, but not on macOS [:(]
Would you be able to run Sweet Home 3D from a Terminal window to report here the messages it will say? Simply drag and drop Sweet Home 3D application in a Terminal window, type back space, copy-paste [font=courier new]/Contents/MacOS/SweetHome3D[/font] and press enter.
You could try also the free version but it will require that you install Java 6 too.