Electrometer amplifier circuits - surface mount or traditional
The point of electrometers is usually very high impedance.  One possible reason for using large components is the larger creepage distances.

Physically large components are thru hole.  With larger size, the dimensional differences due to temperature will be greater.  Surface mount parts don't work well in that case since they are rigidly held to the board.  Thru hole mounting provides some inherent strain relief from dimensional changes.

Of course if your devices were made in the 1980s or earlier, then thru hole or even point to point were the only options.