"The Undroppable Players List" is a list comprised of the top Fantasy players who can't be sent to waivers/free agency. Without this feature an owner who is out of contention could drop a star player for their buddy, who is first on the waiver order, to pick up, therein bolstering their team for the playoffs.
If you'd like to turn it off for any reason, the League Manager can do so by doing the following:
Turn off Undroppable Players List for League Manager leagues (Web Only)
Click on the "LM Tools" tab
Click on "Edit League Settings"
Click on "edit" next to "Player Rules" before selecting "No" next to "Observe ESPN's Undroppable Player List"