There was a purpose to Superman's few words in BvS. Diana ends her movie having concluded that gods shouldn't interfere in the choices humanity makes; she doesn't think she, as a god, should influence them. So she takes a step back from her ideological crusade and becomes a watchful protector. Superman approaches his role as Superman similarly, albeit he's more public, which is why his most significant ideological statements come from him as Clark in the role of reporter.
Why is he concerned about speaking up as Superman? You can see how much the public worries about Superman imposing his will on them. They worry about every act, which would include every word, being construed as political. It's a difficult choice he makes to come forward and speak at Finch's hearing. But he does do it in part because he is asked, welcomed, invited. Then, the only reason we don't get to see him speak is because Lex is determined to silence him and use his decision to engage against him so that trust in Superman can be undermined in the public and in Superman himself.
In fact, the whole film has a thread about the importance of communication or "conversation" as Finch put it, and it suggests that trouble happens when communication breaks down, because communication or conversation isn't unilateral and it's a non-violent way to get at the truth and resolve differences. Clark and Lois both want to report on wrongdoing from Batman and Lex respectively, Perry stymies them because he questions their bias and their evidence. Superman tries to speak at the Capitol, tragedy ensues. Superman tries to talk to Batman, but Bruce is so single-minded that he won't listen and silences Superman with several attacks. He was advised by a victim of Batman's that he only listens to fists, so he even tries a show of strength to get him to stand down and listen. It doesn't work.
Ultimately, it's getting the message of "Save Martha...You're letting him kill Martha," Superman's sacrifice, and Lois' expose on Lex's crimes that turn the tide. In other words, one act of conversation, one action that spoke volumes, and one act of truth through research make the difference sort of like how logos, pathos, and ethos are all valuable tools in persuasive communication.
Given this context and given my affection for the character, I'm definitely excited to see how Superman's speaking evolves going forward.