This is indeed to save on more expensive missiles. A very cheap missile, the APKWS, is augmented with a cheap laser guidance kit to make the APKWS II, a cheap short range air-to-air missile.
APKWS II isn't useful for counter-manoeuvring targets like fighter jets, but it is perfect for one way drones. The Hydra 70 rocket it is build from doesn't have the range by itself to protect a wide area, but an F-15E can carry a number of 7-rocket pods, and has the speed to chase down drones and cruise missiles over a wide area, like a hummingbird zipping between flowers. Depending on loadout restrictions due to fuel tanks, an F-15E could employ 42 APKWS II and a mix of short range (AIM-9X) and medium range (AMRAAM).
All of this requires airborne cueing, which is why the loss of the E3 Sentry is so serious.
https://www.twz.com/air/f-15e-spotted-packing-big-laser-guid...