In a gradual yet transformative manner, many EU member states have, over the past decades, pursued an active welfare reform agenda, encouraged by the European Commission. This reform agenda has focused on social investment, supporting dual-earner families to ease life course and labour market transitions, while making social protection more inclusive in knowledge economies and ageing societies. This paper surveys the long-term shift towards social investment and offers an alternative political explanation, challenging perspectives that focus solely on partisan power and organised interests. It highlights the importance of ideas and policy-learning dynamics across advanced economies, which have inherited significant intergenerational commitments from past periods of passive welfare state expansion.