Because a strong navy is crucial to US interest. A staggering amount of the world's petroleum products flow through the Straight of Hormuz.
Likewise, the majority of China's energy imports and manufactured exports flow through the tiny Straight of Malacca (or else around the countless other islands of Indonesia). If the straight is blocked, they have about 90 days of fuel reserves before rationing begins. That's why China needs force projection in the South China Sea if they want any hope for a Taiwan invasion to be successful.
More generally, US protection of international shipping is supposedly the basis for the petrodollar system.
When it comes to Russia, defending the GIUK gap is also crucial...
The military-industrial complex seems perfectly designed to go after very large and expensive projects. They’re great for creating jobs, keeping the politicians happy. Shareholders love it. And the military is far from innocent: I’ve heard that a common sentiment held by career officers is that you want to always attach yourself to the new, big project, as that’s how you advance up the ranks. Commanding a drone squad doesn’t make you a general.
Aegis ensures his first strike will not be completely successful, while Ohio/Virginia ensure that the counter punch would be so painful it’s not worth starting the fight.
Force projection is incredibly important, as long as we keep our leaders in check.