That is typical construction for a pre-1900 “home made” cabinet base because all one needed to build it was a hammer, nails and a saw. A ruler or tape measure was not needed.
One first determined the width of the cabinet they were going to build (a stick of wood cut to length would work)….. and then the width of the 2 side and 1 center face boards were determined by the width of the single-board doors.
The 2 single-board doors were made first ….. and then the 3 face boards were cut so that the width of all 5 boards would equal the desired width of the cabinet. (length of stick)
And that is why you will never find 2 of those cabinets with the doors and face boards being the same width.