Why jeffersonian world view (that of the yeoman farmer as the bedrock of american democracy and the american economy) disappeared by the mid-nineteenth century ?

Need for industry--the War of 1812 demonstrated the US dependence on Great Britain for manufactured goods. 

Following the War of 1812 and experiences with blockades and embargoes, the US came to the realization they could not be self-sufficient and were dependent on Great Britain for manufacturing. The US government began to invest in industry and infrastructure as well as banking to launch an industrial system. Farming remained important but as a piece of the entire economic system.