Why the swimbriefs has a small lining inside the front?

[zungaboy]

Hi Friends, I have some ideas about why the swimbriefs have a small lining inside at the front (like a triangle), I repeat, “I have some ideas” but really I am not completely sure what are the real reasons.
I think is for not show the shape of the male genitalia, not show the penis when the speedo become transparent when it is wet after to swimming, to keep the penis in a comfortable position and don’t moving to all sides all the day, to dissimulate erections, etc.. But really Someone knows exactly why the speedo have this lining?....