Well, the short answer is, and in no particular order, personal believes, political requirements, external forces such as lobbying companies.

Quite often, I would say that personal believes are the last one to influence decisions, as a politician will weight the options according to wat can get him/her more votes in the next election rather than base the decision purely on science.

But then, there are economic factors too to consider. As a politician, the person making policy decision will look at how much such environmental policy could hurt the economy and business in the short term, long term strategic planning is seldom considered as politicians tend to be in office for a few years only and these long-term policies are changed by the next parliament elected.

Lobbyists are a real factor to consider as well, since they finance the election campaign of these politicians or because the politicians used to work for these businesses that will be affected by the new policies. In the UK, Liz Truss who was prime minister for 6 weeks only, refused to create an additional tax on profits for oil companies when all the evidence pointed to profiteering to the highest order based on the war in Ukraine by inflating artificially the prices of petrol and diesel. Why did she not do that? Before being a politician, she was a senior executive of Shell, one of the biggest players in the oil industry, for many years, and still has friends sitting on the Board of Directors.

The rejection of environmental policies, especially in developing countries, specifically former colonial countries rich in mineral resources, stems from the pressure of large, profitable companies, which means adopting an environmental policy has double-edged losses: the first is its impact on the leaders of countries and their control, and the second is economic losses, which means their bankruptcy.