Nephi notices that he has attracted a crowd. Indeed, it is highly likely that this is exactly what he had hoped to do. He knew that the road to the market was heavily traveled, and he also knew that he could be heard on his tower. Had he not wanted to be heard, he could have offered a quieter lament somewhere farther from the public.
When he has their attention, he begins to instruct them. He takes the opportunity to tell them that they have rejected their God, that they have “given away that the devil has got so great hold upon [their] hearts.” Since one of the signs that the people had rejected Nephite values was the desire for wealth and status, the fact that the people were on the way to the market may have also placed Nephi in a position to preach to those who needed to hear the message, whether or not they would actually hear it.