Missiles have warheads and seekers, different types of seekers target different bands of the IR spectrum.
An AIM-9X is designed to target the heat signatures of engines. It’s sensitive enough to block something like a balloon, but that’s on the edge of the range the seeker can acquire.
Using air-to-air at close range is less risky than trying to use the weapon.
OP and half the retards haven’t successfully flown a paper airplane, but it’s full of fucking opinions about it.
The pilot is irrelevant to the outcome, really. They didn’t choose which weapon to use, probably, and all pilots would have the same problems shooting down the balloons. The missiles are designed to kill aircraft that have a very different radar and IR signature than a balloon.