It doesn't extrude me the central part. . .You miss 17 odds to define that figure, of course everything disappears.
I would also like to understand why you use the spline for the arched part, the spline is the line less easily governable and impossible to reproduce with a traditional machine.
said this, for the problem of extruding only the external part, just define " construction " the two horizontal lines, the splines are not to be combined.