The Right have a great advantage in all politics - they want Power. They don't want it FOR anything, they just want Power. Yes, OK, they also want to get rich and Power helps with that, but basically it's Power itself that gets them excited and lubricious.

The Left used to have an advantage which was their ideology (secular religion). They wanted Power to do things: to free the poor, look after the sick and so on. They had an ideology which gave them what looked like a great gameplan for achieving everything they wanted, the only problem being that it wasn't true.

Their ideology died in 1989. Since then the Left have been looking around for a new ideology and failing to find it. So they can't actually really compete with the Right for Power because they don't care enough about Power by itself.

The Left urgently needs a reason for being. Saving the Earth could be that reason, but most Leftists are too hidebound and old-fashioned to adopt it.