But that's more a matter of pricing. Not the basic parameters of the job.

Building a wall of known size takes X bricks, Y windows, etc. Contractor 1 might have more markup or estimate different hours to complete the job vs contractor 2 but the parameters of the job are relatively fixed.

The dentist is seeing the same mouth (wall) and telling you there is vastly different numbers of cavities (bricks/windows). And not off by a small margin, but orders of magnitude.