I would assume that's because most people right now picture UBI as benefitting only lazy people etc. Once there is a UBI, they'll realize that they're also getting paid, and they'll be more likely to vote against people who want to cut it.
> Once there is a UBI, they'll realize that they're also getting paid
As with existing benefit programs, people will also realize that they are paying. And, as with benefit programs now, even people who are likely to benefit far more from the “being paid” part more than they lose to the “paying” part will often be prone to, and be encouraged by slick propaganda from moneyed interests to, identify with and vote for the interests of those who are on the other side of that equation instead of their own.
