Using Rodinal it may be reticulation and that's how it prints and scans, excessive graininess.
Films like FP4+ are well hardened and it's almost impossible to get the reticulation that used to be seen with films like FP3 and HP3 (Im used them in the late60's), however you can still get surface artifacts which affect how the negatives scan and print, this is called micro reticulation or incipient reticulation.
One problem is modern Rodinal contains free Hydroxide and that softens emulsions, some more than others, if temperature control is strict there's no problems, when it isn't sometimes you get this increased apparent graininess.
It's common practice in Germany and other parts of Continental Europe to use Rodinal at 16-18ºC as they claim that reduces the grain with Rodinal, it reduces the film swelling and potential of these surface artifacts, but in fact has no impact on grain size compared to using a higher temperature with good temperature control at all stages.
You're using Rodinal. Grain goes with that choice.
I can show you many hundreds of negatives processed in Rodinal with excellent fine grain so your statement is a misconception, rather a sweeping statement, choice od developer.film combination and good craft (technique) is the key.
Ian