[Christ]

Many cars have irreplaceable ball joints that are a part of the control arm now. If the ball joint is worn on one of those, you replace the entire arm.

Labor wise, it's cheaper to replace the arm than a ball joint or bushing.

I don't believe your Subaru has upper control arms, only lowers and a MacPherson strut system [the strut damper is also the upper lateral control for the wheel alignment]. That would explain why the shop said 'front' control arms rather than identifying upper or lower.