The system is this way by design. The people who drafted, voted on, and passed these programs did so with disincentivizing its recipients from making more money being one of the goals.
For example, food stamps (SNAP) were made permanent in 1964 as one of the great society programs. WIC came a few years later. I suspect - but have not researched - that you will find this is true for a lot of current welfare programs.
There may be people in power making bad decisions about administering these programs, but I don't believe they were designed to ensnare.