Valve added confirmations. People complained about confirmations under a dollar, so Valve made a dollar the limit. So scammers abused that compromise and people weren't happy that scammers were able to sell things without confirmation and Valve can see what the trends are with scammers. So they reinstated always requiring confirmations and people who think nothing will ever happen to them have opinions and assume theirs are the ones that matter.

Originally posted by ArthaX:

Why do i need to confirmed every transactions on steam?

Because of the scammers.