Complex sentence: Israel was the only operator to use and develop the air-to-ground abilities of the air-superiority F-15 variants, doing so because the F-15's range was well beyond any other combat aircraft in the Israeli inventory in the 1980s.
Split into simpler sentences: Israel was the only operator to use and develop the air to ground abilities of the air superiority F-15 variants. The main reason being its range being well beyond any other combat aircraft in Israeli inventory in the 1980s.