Why did Louis de Broglie and the "old school" scientists think radio waves could be used to explain the atom?

Matters have wave-like behavior which was first demonstrated by George Thomson, on his experiment about thin metal diffraction. De Broglie then soon found out that these waves can help us predict the mass of almost any matter by using his equation, wavelength is equal to Planck constant (h) over mass times velocity. Newton first thought that since light travels in a linear fashion, the light source then emits small particles. However, his corpuscular theory cannot explain interference and diffraction. De broglie, hypothesized that matter has also wavelengths but most are negligible to our eyes since large objects exhibit smaller wavelengths. That is why wave-particle duality exists because both are essential in explaining atomic properties.