Why the swimbriefs has a small lining inside the front?

[Torchwatch]

if you were wearing soccer shorts you would wear cotton briefs underneath to give support and to keep the fabric of the soccer shorts clean.
It is the same with the liner in swim briefs.
Have you ever worn swim briefs or a swim bikini without a liner ?
The Elizabethans wore washable linen underwear under their jewel encrusted outer clothing, they rarely washed their bodies but were supplied with fresh linen.