That's the main difference: in marked contrast to New Zealand (not so much Australia) and like Argentina, Uruguay's native population was dispersed and fairly low-tech. That's partly because of three centuries of sustained contact with Europeans before the beginning of mass immigration into independent Uruguay in the mid-19th century.

Argentina and Uruguay have fairly similar histories, becoming noteworthy polities in the early 19th century, receiving mass immigration from the mid-19th century on, and enjoying resource-driven economic booms in the context of increased social-democratic and other radicalism into the 20th century. Things just diverged most visibly from Australasia in the 1930s, particularly.