During the victorian age, the upper class became very wealthy in part by exploiting the lower classes, why?

No economic regulations: During the Victorian Age, there were no regulations regarding the economy and therefore employers could pay poorly and work their workers for 12+ hours. 

The combination of low pay, long hours, and child labor allowed employers to make big money while not passing it on to the worker. The time was marked by a belief in Social Darwinism, meaning people believed it was natural that some would be wealthy and some would be poor.