That's because only in a perfect being faith would imply action completely. Most lack the inner strength which is why Upanishads say that 'Na Bala hinena labhya (cannot be attained by the week)' what SV would adopt as "if there is any sin, it's weakness."
Same for all religions.
as a Hindu, I feel like majority of Hindus don't really believe in God. they say they do, but their actions don't seem to reflect their belief.