This is so blatantly about 'them' and 'us'. It isn't about getting people to have a 'work ethic'.
It's about saying 'I know you work 50 hours per week at NMW to support your family, but your partner needs to find work too, because you don't earn enough.
Meanwhile, the person who is fortunate enough to be co-habiting, engaged to, married to, whatever, a person who has a well paying job can be told:
'Ahh I know your partner only works 26 hours per week, but they earn a good salary, so you don't need to worry about it...no conditionality.'
Yet, both families have one person working and one not. How is that equitable?