Python was already the #2 scripting language (after perl; not counting Visual Basic) back in ~1994 when I learned it. Tcl was already dying out by then and Ruby hadn't been released. So you basically had Perl or Python. You're right that it was a "first mover" advantage but I don't think data science had a lot to do with it. Perl didn't evolve gracefully over the 1995-2005 period but Python did. I think it is probably as simple as that.
By 2005 or so Python was already the #1 scripting language (other than PHP, I guess).
By 2005 or so Python was already the #1 scripting language (other than PHP, I guess).