Do you have access to the BOM? Sure it was likely a cost-savings measure, but it may have been to combat rising prices elsewhere. It's a two-sided equation and we can't see the whole thing.
If Apple did want to be environmentally friendly though I would think offering a reasonably priced multi-device (4-ports?) charger would be more effective than just selling a single-device charger separately.
One charger for many devices for many years is a better story than "It's the same charger, just purchased separately now."