A geographically large country wants its fighters not just to be able to fly further, but also to have them in as many places as possible.
Geographically large theaters not only concern reach, but also the ability to operate from remote/forward airfields.
Finally - on average, absolute majority of missions(even in high tech, high intensity conflicts) aren't about 100% capability - neither in stealth, nor in reach or payload. This leads us to 80/20 rule:
it's more efficient to perform 80% of missions with smaller aircraft (which can perform them no worse), allowing larger, more maintenance-hungry and longer-ranged aircraft to be concentrated where it matters on what matters.