It was supposed to be a big win for climate activists: another of the world's most powerful mining companies had caved to investor demands that it stop digging up coal.

Instead, Anglo American Plc's exit from coal has become a case study for unintended consequences, transforming mines that were scheduled for eventual closure into the engine room for a growth-hungry coal business.

And while it's a particularly stark example, it's not the only one. When rival BHP Group was struggling to sell an Australian colliery this year, the company surprised investors by applying to extend mining at the site by another two decades — an apparent attempt to sweeten its appeal to potential buyers.