The reason why the bases are being left there. Is because of the idea that it is to costly to bring them back with us. However, the suck comes from the improper analysis.
The proper analysis should be that any bases that Iraq Government soldier's loyal to the people of Iraq can't occupy. Should then have proper civilian agent contractors in the area that sell that type equipment disable the bases. So that it does not fall into Iraq Government radical's hands. This would be easy to do: Simple the Government has on both side of the isle of course, citizens who own business that could easily use a proper where the man speaks fast like, oh ya, auction. In which the equipment before the US moves out of it could be sold to the highest bidder. So then the government know's that certain folks that will use the funds or nicesities against them will not be able to obtain them. As the US could hold down the base while it is dismantled. Then the civilian's could take it to a warehouse and the economy could go on its mary way.