In almost all microphone designs, it's quite simply because that's the way the diaphragm faces.
A hand-held mic has the diaphragm set at 90° to the body, so you point it at the sound.
The standard large diaphragm condenser as in your photos has it in line with the body, so the pickup pattern is ...
Record the two mics as two channels. Then you can decide what you want to do when mixing. As this seems to be very uncommon, there probably is a reason. Only way to know for sure is to test it (takes about 15 minutes, so why even ask here? )