All infrastructure eventually needs maintenance. Whether it's a water system, a bridge, or a school, there's a cost to keeping infrastructure running.
It can be useful to think of infrastructure investment in terms of net investment, meaning the amount of money spent on infrastructure after accounting for normal maintenance. The U.S. Bureau of Economic Analysis keeps track of this number, net public investment, as a percent of GDP. It has been trending down since the 1960s, the Bureau reports, and is near a record low. "The only years with lower levels were 1942–45, when the civilian economy was starved to fund the war effort," Doug Henwood reports in Jacobin.
This shrinking investment in infrastructure leaves less funding for disasters, updates, and new projects. As the country's income has increased, the percent of income invested in infrastructure has dramatically decreased. "To get back to that 2.6% average would mean an increase of $400 billion a year in public investment," Henwood writes.