Sustainable practises, especially energy generation are way cheaper than non renewable sources, so why would corporations try to make energy cost more for themselves?

Sadly, that’s not the whole story. I don’t share all of his takes on how to move forward (he’s a tankie, I lean towards anarchism), but Second Thought summarized very well what the weak point in your argument about cost is: https://youtu.be/3gSzzuY1Yw0

this time the main blame is on the government for not putting the environment first and not forcing adverts for unsustainable products to have warnings about their environmental impact. But the government is installed by people (in democracies) and the people clearly don’t care.

Sadly, you’re also wrong here. For the USA it has been shown that the opinion of average citizens on proposals of individual policies has no significant impact on the probability of the policies being implemented. It is only the position of lobbyists that have an impact. Lobbyists also include environmentalist groups, of course, but more often than not corporate lobbyists all take similar stances whereas non-corporate groups are very often single-issue groups who only make themselves heard on relatively few occasions, making them less impactful overall. https://scholar.princeton.edu/sites/default/files/mgilens/files/gilens_and_page_2014_-testing_theories_of_american_politics.doc.pdf

I don’t know of a similar study for EU countries. My guess is that the multi-party systems here work in favor of more voices being heard but also against implementation of new actually useful policies because of the need for compromise and coalitions.