If people wanted to be practical, then they could use an RNG app installed on their phone.
However, there are some things which are appealing about physical dice where one wants all their RNG stuffs to be of the shape of a die.
Tactility - on this forum, I need not explain why this is valuable. Even if one said a faceted rod would still satisfy this, there is some amount of joy and suspense in seeing a die bounce around erratically.
Aesthetic - a collection of dice with similar designs - albeit different amounts of sides - makes things quite appealing
Storage - dice with similar dimensions can all be lined up neatly in a compact form of storage. (i.e. dice tubes and dice trays) Elegance of storage shares similar thoughts to aesthetics, though this does also appeal to those who value organization.
If you don't know what I'm trying to get at, then look at this picture and judge whether or not any of it makes sense after that