The monotonic IQ increase can be attributed to improved nutrition and schooling. However, most evidence suggests that intelligence is genetically heritable to a large degree. Improved nutrition only goes so far; a really healthy pig still won't have human-level intelligence. At some point, we would expect selective pressure towards being less intelligent to catch up with us. Or, looking at it another way, we might be a lot smarter today if we had both the nutritional and educational advances of the last few centuries and a birth rate that wasn't higher in lower-intelligence populations.

Being poor or jobless has vastly more to do with (lack of) technology and access to resources than it does with your position on the intelligence distribution.