Automation replaces a labor requirement with a capital requirement, so it increases the power of the capital class.

Automation also means fewer jobs, so it increases the size of the precariat. UBI can fix that, but the capital class has no particular reason to care what happens to jobless people, and the precariat is useful to suppress wages, and we just established that automation also increases their power, so it's not going to happen. UBI would make sense under market socialism, which also fails to protect the jobless on its own, but we don't live under market socialism.

And I don't think policy is the best lens to look through for people currently living under capitalism. You could dismantle capitalism with something as boring as UBI + a progressive wealth tax (ask me about it some time), but doing that would still require enough power to dismantle capitalism. You don't gain anything by coming up with a way to get there by passing some laws, instead of unions forcibly cooperatizing the economy, or a vanguard party leading people into a revolutionary struggle. They're all trying to do the same thing, so they all require the same amount of power. For now, it's much more important to worry about how to most efficiently build non-capital power structures.