"The money dried up as the Vietnam was drained more and more money."
Nope, LBJ was perfectly fine with guns & butter as was Nixon.
Remember that the 1970s is when energy prices started to become an issue and global competition in manufacturing from all the countries bombed to the ground in WWII reemerged. The country got squeezed from exponentially increasing welfare costs, warfare costs, energy costs, inflation, de-industrialization, social unrest/crime waves/the emergence of the costly drug culture & anti-drug policies, the rise of NIMBYism, white flight, and worst of all DISCO.
Also remember that it was an era of political instability, with many different office holders coming and going.
All these factors combined made it much more difficult to undertake large scale urban renewal projects as had been done in the previous 30 years.
Boston gave up on building housing and shopping centers for office towers around this time for that very reason. They were the greatest return on investment in a very uncertain time. Same for government office space, it was guaranteed money from a local workforce even if it meant permanently losing property taxes.