With custom cabinets they would be able to fill that gap on the left and also use smaller filler for the bottom cabinet left of the range. For pre-fabricated cabinets they usually only have size increments of 3" so you end up with big fillers. The sink area upper cabinets look like a standard size and the hood cabinet is actually wider than the hood so it definitely wasn’t made custom to this hood.
These people need donations or something!