Millennials are disillusioned because they are tangibly disadvantaged compared to previous generations, a process shaped and accelerated by austerity; lack of job security, burdened with educational debt, no savings, depressed wages, facing a lifetime of rent & spiralling costs. https://twitter.com/FinancialTimes/status/1328659350781571073

None of these issues are tackled - particularly in the UK and US - as governments (and referendum results) are disproportionately propelled into power by older generations, and virtually nobody in power has any lived experience of hardship. These issues are allowed to fester.

"as you get older, you become more conservative" is deeply misleading in this context; living through a broken economic system in which you are inherently disadvantaged leads you to either blame the system or look for scapegoats - migrants, benefit claimants- through gaslighting.

You will not be satisfied with a purely capitalist system - more accurately, one which is unregulated and imbalanced to the extent of removing opportunity and aspiration - if you have no capital or meaningful progression. But current governments have no motive to tackle that.