Everyone has seen a peeling garage floor: coating lifting in sheets where the tires sit, flakes coming up with the broom. Almost every one of those floors was coated over concrete that was cleaned but not ground.
Concrete has a smooth, dense skin on top. Acid etching roughens it a little; diamond grinding opens it up completely so the epoxy soaks in and locks on. That's the difference between a coating that sits on the slab and one that becomes part of it. Grinding also removes old sealers and paint that would otherwise stop the epoxy from bonding.
The system matters too. A pigmented epoxy base coat gives the color and the bond, decorative flakes add texture and hide dust and tire marks, and a clear polyaspartic or urethane topcoat provides the UV resistance and abrasion protection that keeps the floor from yellowing or scratching.
Expect a two-to-three-day process: grind and repair, base coat and flakes, then clear coat. You can walk on it the next day and park on it after about a week. Done right, it's a floor you'll sweep, hose, and forget about for a decade.