"Hostile intercept by ground to air missiles."
When they are within the range of launchers. Which usually move far slower than airplanes, when needed. Also, you need to hope their SEAD airplanes (or drones) didn't wipe them out already.
Usually SA systems are only good to defend static targets (preferably with fighters around to help), or slowly moving ones. Also, missiles able to engage targets far enough are usually large, expensive, and launchers may have limited spares. A plane can engage at larger distance, deliver a missile closer, and from a better position to hit.
Even your ground attack drones may require help to deliver their weapons before being downed - manned or unmanned, or they could become easy targets.