My understanding from a ex colleague who's wifey is a hoarder on how it was started -
They start small eg a few pieces of pamphlet without a clear objective. Perhaps lazy to throw them.
Next they increase to more pieces.
When it forms a stack, they start to think it can be sold for money.
Next they started to look for more, and the more they collected, the more kicks cum, as it means more money otw.
After a few years, his house was piled with pamphlets in 1 room.
Next, they will look for something else.
And the same cycles leepeats until the whole house are piled with rubbish.
Some will stop here while some will extend to the outside of their house.