Because it's just that simple.
They are doing exactly that. They are upping the work requirements, which means they are basically going to nullify anyone who can still breathe unaided from seeking benefits. They are abandoning an entire generation of young people to homelessness with the Housing Benefit age cap. They will in all likelihood double the Bedroom Tax, effectively making social housing unaffordable for countless thousands of people, disproportionately hitting the disabled.
Again, people simply do not realise how big a chunk the £12bn cut is. To give a clue, it regresses the spending levels of welfare as a whole to pre-2007 levels - it's like a monster recession for welfare that will not recover, as it takes away the very infrastructure.
I just feel desperately sad for those who genuinely rely on state support to live. Politics shouldn't be played with peoples very health and lives - it should be the bare minimum government should protect.