How Macbook Pro detects an external microphone through TRRS jack?
The phone senses the impedance between the 2nd ring and the sleeve. Plugging in a "raw" connector is no different than nothing plugged in at all. There is still practically infinite impedance between the 2nd ring and the sleeve.  That is why it doesn't detect anything.

Note that if you insert a traditional TRS plug into the jack, the sleeve will "short out" the 2nd ring position. That indicates to the phone that earbuds (or headphones, or interface cable of some sort) has been connected.
If you connect an electret microphone capsule between the sleeve and the 2nd ring, then the phone should recognize it.

Note also that earbud/mic gadgets with remote-control buttons use the microphone connection to temporarily insert different resistors into the mic circuit. The phone monitors the impedance and when it sees it change, it identifies the button press and proceeds to take the appropriate action (skip, volume up/down, etc.)

Ref: https://en.wikipedia.org/wiki/Phone_connector_(audio)#PDAs_and_mobile_phones