"Where do you get the idea that Homer/Shakespeare are more influential?"
Oh, just Homer's epics arguably being the most foundational works in Western Literature alongside the Bible and Shakespeare's being the most quoted playwright in the world, most cited English author, and the fact that he's influenced everyone who came after him, whether they loved him (Eliot, Dostoyevsky, Woolf, Faulkner) hated him (Tolstoy) or had complex feelings towards him (Lawrence, Shaw, Twain, etc.)
Shakespeare's characters are the most recognizable in the world created by a single author--really, only Dickens and a handful of others can even challenge that, and Vergil isn't in that handful.
What's more, he has influence over multiple fields, not just literature--
Freud considered Shakespeare's characters when forming his concepts of psychology...
Marx considered Shakespeare's works, using them in examples of his arguments regarding class struggle,
Just about every feminist author and theorist has turned to Shakespeare at some point.
Put bluntly--
Even if we wanted to say Vergil and Shakespeare have similar amounts of influence and talent...
Shakespeare achieved that degree of influence in just 397 years, whereas Vergil's had 2,000 or so years to accrue in popularity.