That's different, the mechanic gets money from you directly (the physician analogy is not relevant in many countries). The people writing these reports are NOT getting a direct benefit from th reports. It's a lazy statement of someone unaware of their function. Most likely it's a group of people from academia, public works and yes industry that make the point. While the guys from the industry may have some monetary interest, it doesn't affect the other groups.
Actually, if you bother reading those reports, you'll find out that what they advocate is not waiting until things are about to crumble to make the investment because the work is so close to being a rebuild that it's much more expensive over any given period of time to do so than quickly making a little patchwork early on. The reports actually advocate spending less money on repairs... by doing them in a timely manner. So the entire analogy is flawed.
You don't even need to be a civil engineer to understand it either. If you've ever lived in a house whose owner decided to not spend the money to fix a little leak in pipes, or in the roof only to have to dish out an order of magnitude larger amount of money to fix the damages resulting from the neglect, then you have a healthy appreciation for the soundness of the advice.
But Infrastructure spending is not sexy, as John Oliver would no doubt agree.