Why do people think petitions never work?

I have signed a few petitions in the past on Change.org (just signed one a week ago about convincing DeviantArt to bring back their old layout), however I’ve noticed that some people on the internet-including Change.org-are saying that petitions never work.
 
Why do they think that? Why do they doubt that petitions will work, even when a majority of them do?

@DragonBoi471  

 
Citation needed

Politicians are not obligated to do anything the petition says (I could be wrong). I have no faith in my heart for anyone in a higher position as well, so it may just be bitter feelings.