The rich people is due to a nice job.
想要表达的意思是：富人之所以富,是因为有份好工作.
而不是：富人是由于有份好工作.
所以,这么说有点问题.
比较贴切的说法是：
Their wealthiness is due to a nice job.
他们的富有是因为有份好工作.