With the caveat that I have not yet seen the film, as indicated by Edlothiad and DisturbedNeo, the use of silence served two purposes, both to help us share the protagonist perspective and to set up a later reveal for the audience.
Both protagonists have been deafened from the explosion. For this reason, we get a muted scene to reflect the perspective of the characters, isolated by their lack of ability to hear. Wonder Woman, due to her Amazon prowess, heard more of what was being said than she realized, but it took a while for her to recover from the explosion rattling her.
Out of character plotting
The second reason is that it sets up the revelation that Steve declared his love to Wonder Woman during the scene. If introduced earlier in the film, this revelation would have flavored the viewer's interpretation of the following scenes, and would have cheapened her realization of his declaration, which gave her a heroic second wind. One could even argue that, without this coming at just the right moment, she might have arrived at the final battle having already used up that inspiration and lacking the final push that allowed her victory.