[wl]

These cranks are aluminum. The problem is that they are a hollow clamshell design to save weight. The bonding of that clamshell design is problematic.

[jeffbee]

The newer hollow cranks aren't problematic, so it can't be just that it's difficult to make a hollow crank. And it's not even that fancy any more, considering that the $100 FC-R7000 is also hollow.