Why were Keynesian policies abandoned?

OECD countries switched from Keynesian policies to supply-side policies from the 1980s. As they now return to Keynesian policies, it is worth asking why they had abandoned them: One explanation is ideological: the determination of capitalism, from the 1980s, to favour the interests of shareholders, which led to weak wage growth and a slowdown in public spending to reduce the tax burden, the opening up of trade with emerging countries and the free movement of capital; Another explanation is economic: in the 1970s and 1980s, demand stimulus at a time of rigid supply simply led to inflation. The idea therefore came naturally that supply-side policies were needed and that, in particular, the tax burden had to be reduced. The challenge today if Keynesian policies are to make a comeback is therefore clear, if one refers to the motives for abandoning them in favour of supply-side policies: They must not have a negative effect on supply; If possible, they must even increase supply (the case of efficient public investments); Bearing in mind that they will inevitably reduce the return on equity for shareholders (if there is faster wage growth and tax on capital income is increased).