[usrusr]

Because of the U in UBI. Conventional benefits pay for proof of need, they reward incapability. A terrible incentive.

[speedplane]

But universal benefits pay everyone, which remove all incentives.

[usrusr]

The U removes the incentive to seem/feel incapable. Positive incentives stay, except maybe working to not starve, but that one is already eradicated with conventional benefits.

I haven't seen anyone advocate a "exclusive universal basic income", where other forms would not exist.