Well, you asked why it didn't show up in "ifconfig" and the answer is "because it wasn't 'UP'".
When you do "ifconfig -a", it is there.
Note, incidentally, that in the old days, "UP" and "has an IP address" were synonymous. Nowadays, however, I've noticed that it shows as "UP" even when it doesn't have an IP address. I treat this as an anomaly.
And some folks need to stop being fanboys and see the forest behind the trees.
(One of the best lines I've seen on this board lately)