Why don’t recessive traits always eventually disappear from populations?

Because the recessive trait might not show, but its there, lets say B is brown eyes and b is blue eyes, BB is brown, Bb is brown, and bb is blue, if B is present, brown will always show, but as long as the little b is there, there is a chance of the kids having blue eyes, sure most people would have brown eyes, but a lot of the people with brown eyes would be Bb