Big difference is that Oda actually likes to write plots for Usopp. Usopp is a flawed and nuanced character, and therefore way more interesting for an author to work with; with Zoro is obvious Oda simply doesn't care as much as he doesn't find him rich enough, hence why, at the end of the day, his role in Wano was ultimately shallow in spite of the potential he seemingly had. But Usopp? Oda likes Usopp so much that his best piece of story so far revolves around Usopp, and even when the plot doesn't require it he's willing to give him very important roles (such as Dressrosa). Practically the whole story is splattered with exploring Usopp's character. Also, just like Zoro isn't exciting to work with for storytelling, Franky is entertaining in fights as that's where his gadgets and personality arise —hence why he pretty much always gets a fight, whether it's Fukurou, Ikaros, Baby 5 and Buffalo, Señor Pink, Sasaki; Oda enjoys drawing fights for Franky and clearly has fun with him, but he isn't as interesting to develop as Usopp.
I highly doubt Oda will waste the chance to fulfill Usopp's connection to Elbaf. Don't compare a character he likes from an authorial point of view to Zoro and Franky, these two have nothing over Usopp in this regard. On top of it, the build up for Usopp's role in Elbaf is arguably one of the strongest in the whole series and has been brought back again since Little Garden. It's not something Oda would just forget about.