Because we can 'afford' 0bamacare.
Except that we can't. We also can't afford a dozen or so welfare programs for parasites foreign and domestic, a ponzi scheme masquerading as a retirement program, regulatory agencies galore, bailouts for failed industries and poorly considered loans ...
Get rid of all that unconstitutional crap, and we'll have no trouble affording a decent Navy. And a decent Army. And a decent Air Force. And decent border protection.
Maybe I should have put in a “/S”?