Good point, and there is another twist I realized: sugar is used as filler (e.g. for removed fat in low-fat stuff), so Erythritol might not work because same volume of it would make it unbearably sweet.

Personally, I'd prefer they just kept the original fat and call it a day as there seems to be absolutely nothing wrong with it health-wise.

You are both thinking of other sweeteners, like sucralose (Splenda).

Erythritol is actually 70% as sweet as sugar. So you actually need to supplement it with something else to match sugar.