Did Apple claim this was about the environment? I don’t recall that and it wouldn’t make sense, as they just swapped the newer cable for the old cable and didn’t reduce the number of parts. It does have a benefit for SE owners if they prefer the newer cable and want to plug it into their newer Mac that doesn’t include USB-A, while it doesn’t benefit an SE owner if they want to use an old USB charger. I’m truly surprised so many MacRumors readers are so attached to keeping old legacy chargers. If you are truly that concerned about the environment, you shouldn’t be upgrading to a new watch/phone/iPad that includes the new cable, and just stick with the old one that goes with its charger you want to keep and save the environment even further.
As for the cost savings for Apple, well, duh. Of course they are trying to up profit. And if you don’t think they would bump the price up equivalently if they put the charger back in the package, I’ve got a bridge to sell you that would look great with that new Apple Watch SE you bought.