then have a think about the relationship between wavelength and the size of the smallest features you're able to image
Increasing the frequency decreases the wavelength.
When wavelength decreases, it can penetrate more and help us visualize smaller things, right?
Is this the reason we can't see atoms because the wavelength of the light is bigger than the size of the atoms which means they cannot penetrate enough so that we can see the atoms.
I hope I was able to get my point across.
*afaik you get more attenuation i.e. less penetration with shorter wavelength ultrasound https://radiopaedia.org/articles/attenuation-ultrasound