I'd argue the difference between private companies and government is that in government that spending is public.

Spend a few mil on something of marginal utility, politicaly controversial, or funding a study for something that seems obvious? Congratulations! Fox News found it on USASpending.gov (maybe not now that 18F is dead), and is drumming up outrage. Now your fielding phone calls from senators who are looking to grandstand by reducing your budget.

Waste a few million on a Salesforce implementation that never works, never does what it promised and never gains adoption and is finally quietly abandoned? Doesn't even make the Shareholder meeting and the exec in question gets even more influence for his ability to lead large projects.