The "poor are lazy" is just the other side of the idea that "wealth is the product of merit".

The wealthy and the institutions they own (including most of the Press), in the process of pushing to society the whole bundle of ideas around them being deserving of the privileges they have and that discrimination by wealth is fair, just slander the poor as lazy for the sake of little more than consistency (since things like Social Security cost way less than corporate subsidies, tax evasion by the wealthy and the myriad of tax avoidance backdoors in the tax systems of almost all countries that are only accessible to the ultra-wealthy).

Also, of course, pushing the idea that working hard can make you rich is part of pushing the whole idea that "wealth is the product of merit", hence "the poor must work harder". This idea is of course absolute bullshit - just local at social mobility rates in your country - though in some countries (for example the US) it used to be true (as the US used to have very high social mobility, whilst now it's very low).

Anybody who digs down finds that behind pretty much every rich person there is a rich parent or, at best, a priviledged upper middle class upbringing - wealth in the modern society is overwhelmingly NOT the product of merit, it's the result of luck of birth.