The literal purpose of UBI is to ensure that taxpayers do owe each citizen a fixed amount set at an average living. Making that a social obligation based on birthright rather than a potential future entitlement based on need is how it's different from social insurance schemes. The assumption if you're able to work and not interested in looking for it you probably don't need the money as much as other people certainly isn't what's wrong with current welfare states.
You don't have to believe that "folks not working are immoral" to believe that helping those fortunate enough to be able to choose not to work at the expense of those that aren't [whether by reduced benefits or higher taxes] isn't what welfare states were for.