If people could vote themselves more money the voter turnout would be insane. How would anyone control something like that? Anyone who ran against the increases would be easily defeated with something like this: "My opponent wants to take the money you deserve!".
At some point you would be giving people more money than you produce as a country and then it's only a matter of time until the money runs out. Once the money runs out then your government will evaporate as the enraged populace tries to pin the blame on one group.
This of course is on of the central issues with government run wealth redistribution programs, nobody wants less money and they will go to the polls to protect it. Whatever you think of the ACA/Obamacare in the US, once it got established and started paying out there is almost no way to repeal it as no one wants to lose their benefits. Even establishment Republicans learned their lesson and are now leaving it alone after seeing that they angered many Americans who enjoyed those benefits and threatened their chances of being re-elected.