Did you ever watch "Hoarders" on TV? This is a deeply seated emotional issue and there is precious little chance that a simple persuasive chat or argument will provide any meaningful progress.
My wife's aunt was a world-class hoarder and at a point her health/mobility needs took precedent over the need to keep stuff. She acknowledge/admitted/accepted the fact it needed to be done and a small army of very caring family members spent several days tossing tons of stuff. When the aunt was out of the hospital, she missed some things but felt greatly relieved to be home with much easier mobility/household management and genuine caring and supporting family. Without the health event as an emotional trigger, no way the house have been cleaned up.