The issue with unguided bombs or ground strafing is that you need your aircraft to fly at relatively low altitudes to accurately target even those sort of fixed relatively large targets.
Flying at lower altitudes exposes them unnecessarily to lower altitude rudimentary air defense systems like AAA or MANPADS.
The benefit of PGMs is if you are able to suppress or defeat enemy long range or medium range air defenses, it allows you to be able to defeat targets with impunity, without exposing your valuable fighter aircraft or strike fighter to low altitude short range air defenses.
My point is that they are useful after enemy anti air has been suppressed if you can afford the sorties rate.