Capitalism requires a reserve army of labour, UBI would never exist as being unemployed has to be punishing. The working class can demand reforms but eventually these reforms will bring it into conflict with capital and it would be more likely than not before a livable ubi. The dole however is a thing in many places, but generally your still in poverty on the dole.
It's better to struggle for winnable reforms that are won by building workers power, which then train the working class to become self determinate and change the face of society forever.
Ubi is only ever advocated for by people who wanna vote for some lib to hand it down, this does nothing to build the workers movement