Form v function...
For a designer..... the Function would be a metaphor. The Form (if gears would work) is unimportant.
For an engineer that's reversed - an engineer would be concerned if the gears would work (Function).. doesn't matter how the look (Form).
Designers are concerned with how things look, how easy things read, how dynamic things appear. In most cases... It honestly does not matter if gears would actually be functional, they just need to look nice and maintain overall design continuity. I wouldn't chalk this up to "laziness"... at least not that I've seen.. ignorance, maybe. But more realistically is lack of software knowledge to get accuracy.. or time constraints preventing the acquisition of the necessary software knowledge. Most designers/illustrators I know are fully aware when they have gears which would not actually function.... "they still convey moving, tools, working.. that's all I need."
- If I draw a car, I don't worry about measuring things to ensure the tires are proportionately sized to the frame...
- If I draw a bell, I don't worry that the clanger is sized correctly based on the bell circumference....
- If I draw a rocket ship, I don't worry that the structure is aerodynamically correct or even possible...
- If I draw a microphone... I don't worry that the wire mesh covering one end is the correct spacing and proportion as related to real world microphones...
... I just draw what looks good and works for my needs. It just has to look like what I intend. It's not a blue print or schematic.
I would only concern myself with functional gears if working on a piece that is destined to be seen by engineers, mechanics, etc... readers that would be fully aware of mechanical flaws in artwork. Just as if working on a medical piece, if I draw a stethoscope, scalpel, etc., I ensure they are accurate as they relate to the overall style of a piece.
Ultimately, functional gears or not greatly depends upon the intended audience. I used a gear image today in fact.. but it was for a financial piece ... a piece where no one is expecting some mechanical apparatus to be part of the pitch. It's inherently understood to be a metaphor. Therefore gear accuracy was unimportant.