Modern IAD doctrine for contested battlespaces tends to emphasize protection of assets as a first-order concern - that is, the regional commander will probably set things up so that one early-warning asset (AWACS or ground/sea based, doesn’t really matter) acts as overwatch/a canary, which can then orchestrate activation and firing of SAM batteries. In that context, you very much want to avoid simply having the SAM battery radars (of any type) radiate, because that’s a great way to get a beam-riding HARM missile lobbed at you. SAM batteries tend to use their radars only when they’re confident they largely control the airspace, or when they know something’s incoming and have a rough direction to look towards.