Combos, or combinations, get their name as they combined the function of the chemise and drawers. In the 1900s when fashions started slimming down, the number of layers of clothing a woman needed was less. So combos made the chemise obsolete.
As the combo (and the chemise before it) was worn to protect the body from the corset, when the corset disappeared, so did the combo. It was replaced by the teddy, which had a crotch, unlike the open crotch drawers and combos.