I think Avdol made a point in the first episode about Jotaro being able to manifest Star Platinum quite vividly, and linked it to the strength of his spirit (so, not strictly in a physical sense).All that being said, a Stand? Why this Stand and not others? Its not like it was strictly better or super powered compared to other Stands so far. Seems hard to justify here but not elsewhere - was it just because it was so large?that anybody can see
For this one stand, strength being its defining characteristic, it would be the same: a manifestation so vivid and so "solid" to
be visible to everyone