OP literally stated their own definition and it's all about state intervention in the economy.

Seeing as housing is one of the largest sectors of the economy and personal wealth, I would say it's a huge economic intervention to provide cheaper housing.

Liberals not wanting to provide that much housing is for the reasons you stated - they don't want to interfere. They only give a shit about the appearance of social liberalism, they don't actually want to change people's material conditions.