Why the higher the signal frequency is, the more easy is it to reflect?

The higher the frequency, the shorter the wavelength, then without care, some long wires would become transmission lines without impedance matching => more reflection occurs.

The main reason that higher frequencies are more reflected than lower frequencies, is because higher frequencies penetrate harder materials, and they are reflected. Higher the frequency, more equivalent optical physics phenomenons (reflection, refraction, diffraction, etc) applying.

check this:
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