1. It's extremely unfair
2. It punishes those working to get ahead
3. It creates 'welfare cliffs' where people become worse off for getting jobs. Losing Medicaid is the best example of this.
4. It makes the program exponentially more expensive to maintain because you have to hire people to track who gets it and who doesn't, look for fraud, monitor for when the income threshold needs changed, etc..
It's just terrible policy all around. We learned this during covid. It's so much easier to write people a check and tax the the high earners more to make up for them getting a check.