Bump = All WTBs in one place with zero transaction fees
Posting a WTB / want-to-buy post in a Facebook Group or online forum is incredibly unreliable. Posts are easily lost, restricted to the group they've been posted in and its almost impossible to refine your search.
Bump has all WTBs in one place meaning its easier for sellers to see what buyers want. Buyers get what they want faster and sellers can find a buyer almost instantly.
There's NO FEES and selling your stuff is as simple as sending a message.