Well, because the thickness on the soap bubble is on the order of the wavelength of visible light, which causes interference that we can see. Windowpanes are far too thick for this to occur.
If you look at the treatment of this on Wikipedia or a physics text it is the phase difference beteween the front and back reflections which matter and not the total path length.
Even for a windowpane there will be some wavelengths where the two waves are in phase and others where they are out of phase. The true explanation is that for a windowpane these two kinds of wavelenghts are clustered densely together and therefore even for tiny wavelength ranges the interference effect averages out.
The different wavalengths make only up for color. Some wavelength will have destructive interference and go missing. As the eye is quite sensitive to that you will see a colored surface, whichs color changes with view angle (as different wavelengths will cancel for different angles).
Okay not monochromatic, but very narrow bandwidth peaks
If d (width of the window) is large. Small changes in the wavelength create large differences in phase.
So if you have say light in the range 400 to 401nm coming through the window. There are peaks and troughs in that range, but overall there is no effect.
Light sources are like that in general, they’re not 450.00001nm but some Gaussian distribution around a point. And within that Gaussian there are peaks and troughs but they cancel out.
That was my understanding anyway...