The bushing is what amounts to a heavy duty rubber washer. It isolates metal things from each other, that are intended to move about a bit. If you bolted them hard together, there would be wear, metal fatigue, and metal fractures or failures.
Your shock bushing is in the photo below. It's in the lower center of the pic, the round black thing with the cracks all around it. There is a big shiny metal washer on top, and the top of the shock (threaded rod with the oval-ish shaped end) sticking out with a nut on it. Rubber of any kind only lasts so long, and clearly this one is past the end of its service life. It's a no-brainer that the shock is also at the end of its service life - nobody would put on a new shock with an old bushing. That's why I suggested you replace the shocks. Suspension is one of the non-negotiable things to make sure your car is working right or you will have severe problems. As in crashing your car.
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