Why are fighter pilots seated and not reclined?
Fighter pilots are far more reclined than you might think.

But seat angles are limited by the need for good visibility.  Pilots frequently need to look to down-and-sideways, down-and-forward, and towards their back-quarters.  These are angles that your F-1 Driver couldn't possibly see.

Also, High-G maneuvers are quite rare.  Most modern military planning is about making sure pilots are never even in a position where they need to evade a missile or dog-fight another plane.