Indeed. When I was studying economics in the early 90 it was pretty much gospel that monetarism was right.
The simplest answer that I can offer is because Thatcherism had gained ideological hegemony in the UK (and also the US) in the 1990s and the decade that followed, with the Labour Party's defeat in the 1992 election being seen as indicating that 'there is no alternative' - not least to certain members of the Labour Party itself.
As with my housing example the question remains: Why did none of her successors Tory or Labour act to reign in the financial markets?
In this intellectual atmosphere, those who spoke out against the power of finance were ignored, ridiculed, or simply sidelined by those who possessed a fanatical faith in the 'free market' (i.e. the power of money), while the rest simply followed the tide. One account of the rise and triumph of these 'market fundamentalists' is the following:
The God That Failed: The 30-Year Lie of the Market Cult
Beginning with Margaret Thatcher’s election in 1979, government after government — and party after party — fell to the onslaught of an extremist faith: the narrow, blinkered fundamentalism of the “Chicago School.” Epitomized by its patron saint, Milton Friedman, the rigid doctrine held that an unregulated market would always “correct” itself, because its workings are based on entirely rational and quantifiable principles. This was of course an absurdly reductive and savagely ignorant view of history, money and human nature; but because it flattered the rich and powerful, offering an “intellectual” justification for rapacious greed and ever-widening economic and social inequality, it was adopted as holy writ by the elite and promulgated as public policy.
A more complex answer would consider the influence of high finance on government policies, the effects of the Soviet collapse in discrediting the role of government in the economy, public annoyance with bureaucracy, etc... etc...