Gotham's version of Harvey Dent never became the supervillain known as Two-Face, but why? Debuting in 2014, Fox's Gotham may have at first seemed like a simple Batman prequel, but as the seasons went on, it became something else entirely. Gotham basically existed in its own pocket universe that was separate from all other DC movies and TV shows since the way its story unfolded and characters evolved stood apart from those other DC adaptations. Gotham was its own beast, and that was especially true for its use of established members of Batman's famous rogues' gallery.
Over the course of Gotham's run, Batman introduced villains both major and minor, including The Riddler, The Penguin, Ra's al Ghul, The Mad Hatter, Mr. Freeze, Bane, and more. Catwoman was also prowling about, but she was at worst an antihero. The Valeska twins Jerome and Jeremiah also substituted for The Joker. One major villain that never became a part of Gotham's story is Two-Face, despite Dent (played by Nicholas D'Agosto) being introduced in season 1 and made a series regular in season 2.
In fact, not only did D'Agosto's Dent not become Two-Face, he got no resolution at all, simply disappearing from Gotham after the season 2 finale. Considering he was the only top-level Batman villain to have no presence on Gotham at any point, many viewers likely wondered why Two-Face was missing. For his part, Gotham showrunner John Stephens offered an explanation for Two-Face's absence (via Cinema Blend) in 2019:
"It was tricky because we were bound by the fact that Harvey Dent only became Two-Face when Batman is already on the scene. We did think some times about doing a sort of proto-Two-Face, but never really found the right take."
Stephens' explanation for why Two-Face never appeared on Gotham makes logical sense. The problem is that, when viewed through the lens of Gotham as a whole, Stephens' position doesn't hold up. For one, nearly every villain used on the show - with special exceptions like the famously long-lived Ra's al Ghul - didn't exist in the standard DC universe until after Batman did. That's why it felt so weird when Gotham started having Riddler and Penguin running around when Bruce Wayne was still a child, although audiences did eventually adjust. The idea that Batman's existence was somehow necessary to facilitate Dent's transformation into Two-Face, but not the rise of any of Gotham's other villains, is highly questionable at best and outright laughable at worst.
One wonders if there was another underlying factor in play, such as D'Agosto possibly having second thoughts about staying on Gotham for the long term. To be clear, though, that's just speculation. For what it's worth, not long after D'Agosto's time on Gotham ended, he began playing the leading role on NBC legal comedy Trial and Error, which ran for two seasons. If there was a scheduling conflict there, it could go a long way to explaining Dent's sudden departure from Gotham. As it is, Stephens' reasoning for Dent's (and Two-Face's) absence from Gotham just doesn't make sense.