Their assets are mostly loans to people and businesses, which can’t be used by the banks to invest in renewable energy. They can decide not to lend money for new coal mines, which they have already done, but they can’t tell their customers what to do.
That’s because investors have a longer-term focus than politicians, and are genuinely worried about what happens in 2050. Most CEOs are like politicians, of course, but their shareholders are calling the shots.