Labour is different from capital; the output of labour is meant to upkeep life, and in order to keep labour going, the returns are used to enrich labour in different ways. It could be investing to enhance skills and hence quality of labour; it could be food for sustenance and continued provision of labour; there is also enjoyment and entertainment, that labour needs to have meaningful life. The returns on labour is not to have more labour, nor to expand labour, but to live, to enrich life of labour.
Labour also has fixed lifespan; it needs to be utilised or it gets wasted. It cannot remain stationary or stagnant the way capital could. It does not hold its value when it is not being worked. And being worked, it accumulates greater value more quickly. Hence, labour can be chasing something more basic and yet more elusive than what capital chases.