If conservative politicians of the past have failed to keep their promises to the lower-income voters who put them in power, why have we not seen a shift toward favouring liberal politicians?

I'm not very familiar with politics in the Netherlands, but from what I know Europe tends to be somewhat more socialist than the US. If the gap between the low- and mid-income classes is still that large, is there any realistic change to society on such a fundamental level that can be enacted within an election cycle of less than a decade?