Because they had no idea what was going on, and they really care about the future.
'Time is Running Out,' American Petroleum Institute Chief Said in 1965 Speech on Climate Change
And 1965, according to a letter by Stanford historian Benjamin Franta published this week in the peer-reviewed journal Nature, was the year that President Johnsons Science Advisory Committee published a report titled Restoring the Quality of Our Environment, whose findings Ikard described at that years annual API meeting. One of the most important predictions of the report is that carbon dioxide is being added to the Earths atmosphere by the burning of coal, oil, and natural gas at such a rate that by the year 2000 the heat balance will be so modified as possibly to cause marked changes in climate beyond local or even national efforts, Ikard presciently added, according to excerpts from his speech published in Nature.
https://www.desmog.com/2018/11/20/american-petroleum-institute-1965-speech-climate-change-oil-gas/
Exxon Confirmed Global Warming Consensus in 1982 with In-House Climate Models
Over the past several years a clear scientific consensus has emerged regarding the expected climatic effects of increased atmospheric CO2, Cohen wrote to A.M. Natkin of Exxon Corporations Science and Technology Office in 1982. The consensus is that a doubling of atmospheric CO2 from its pre-industrial revolution value would result in an average global temperature rise of (3.0 ± 1.5)°C. (Equal to 5.4 ± 2.7°F). There is unanimous agreement in the scientific community that a temperature increase of this magnitude would bring about significant changes in the earths climate, including rainfall distribution and alterations in the biosphere.
https://insideclimatenews.org/news/22092015/exxon-confirmed-global-warming-consensus-in-1982-with-in-house-climate-models/
Big oil and gas kept a dirty secret for decades. Now they may pay the price
Exxons chairman and chief executive, Lee Raymond, told industry executives in 1996 that scientific evidence remains inconclusive as to whether human activities affect global climate. Its a long and dangerous leap to conclude that we should, therefore, cut fossil fuel use, he said. Documents show that his companys scientists were telling Exxons management that the real danger lay in the failure to do exactly that.
https://www.theguardian.com/environment/2021/jun/30/climate-crimes-oil-and-gas-environment
The Big Oil Side Hustle: Where 'Renewable' Money Is Really Going

"Last Year" - 2019.