Affording the rig is one thing. A fire department trying to choose what's going to be on it is something completely different. Small departments might want each station's first-out vehicle totally independent of the rest of the fleet. Some call that a common standard of care. Contrast a first-in unit that can do it all with many departments' specialty apparatus, which have their own problems.
Many departments have specialized rigs to the point that they are all single-purpose apparatus.
You'll see tankers that can't self-fill. Crews have to decide before every call which fire truck to take. First-in units might not carry enough hose to reach the closest hydrant. Crews drive apparatus without floodlights and generators. On the fireground, a crew might notice that the needed ground-ladder is still back at the station.