More than subsidizing humans, it actually pumps money directly into automation. Currently the value prop of an automated solution to companies is the total cost of human labor it replaces. If humans get more expensive, the machines/software looks more appealing to implement.
Machines work 24/7, never get sick, and don't unionize.
Why then tie it to labor at all, why not the full UBI? Also why tax credits - many low wage jobs aren't well served by annualized refunds (you can see that in stats where medical visits surge for a bit after tax refunds...).
A UBI of course has a lot of other benefits (being distributed monthly or more often, going to people who are unable to work, being universal and therefore more resistant politically).
Because a negative income tax increases labor market attachment, giving workers more skills, work experience and pride and increases the number of people working. A higher minimum wage on the other hand reduces the number of people working and has no positive effects on employment or skills. From a politician’s perspective a minimum wage is superior because the link between a higher minimum wage and greater unemployment is opaque but that from subsidizing employment is quite direct. Also all of the social cost of subsidizing employment is borne by the government while that of the reduction in labor supply and employment is borne by employers who can’t find workers and potential employees.
You’re right that annualized refunds are far from ideal. Monthly would be better.
Machines work 24/7, never get sick, and don't unionize.