Why does ginger (sometimes) help with nausea?

There's a reason that ginger is so frequently recommended to people (especially pregnant ladies) suffering from nausea--it often works. Not much, but some, per this review published in 2014:

Twelve [randomized controlled trials] involving 1278 pregnant women were included. Ginger significantly improved the symptoms of nausea when compared to placebo (MD 1.20, 95% CI 0.56-1.84, p = 0.0002, I² = 0%). Ginger did not significantly reduce the number of vomiting episodes during NVP, when compared to placebo, although there was a trend towards improvement (MD 0.72, 95% CI -0.03-1.46, p = 0.06, I² = 71%). Subgroup analyses seemed to favor the lower daily dosage of <1500 mg="" nbsp="" span="">ginger for nausea relief. Ginger did not pose a significant risk for spontaneous abortion compared to placebo (RR 3.14, 95% CI 0.65-15.11, p = 0.15; I² = 0%), or to vitamin B₆ (RR 0.49, 95% CI 0.17-1.42, p = 0.19, I² = 40%). Similarly, ginger did not pose a significant risk for the side-effects of heartburn or drowsiness.

https://www.ncbi.nlm.nih.gov/pubmed/24642205

Ginger only helped me a little when I was pregnant, but it did seem to help. Maybe it was the placebo effect, maybe not. Unfortunately, now I associate ginger with pregnancy nausea, so I feel grossed out when I see the ginger pregnancy teas still floating around in my spice drawer.

On my last YouTube video, a woman commented that a peppermint and lemon tea helped get rid of her morning sickness. It turns out that peppermint oil speeds up gastric emptying (https://www.ncbi.nlm.nih.gov/pubmed/17653649), which as discussed in the previous post, appears to be delayed during pregnancy. In fact, HCG inhibits gastric emptying (https://www.ncbi.nlm.nih.gov/pubmed/23197744). If sulfite is building up in the stomach and bringing on nausea, emptying the stomach faster is a good way to get rid of the sulfite and the accompanying nausea.

And guess what else can speed up gastric emptying? Ginger. (https://www.ncbi.nlm.nih.gov/pubmed/11876024)

Which leaves me wondering why doesn't ginger help everyone with nausea? Is it because too much sulfite is just too much even if gastric emptying is sped up? Is it because sulfite in large amounts irritates the upper small intestine in a way that causes nausea, too? When we vomit, we don't just expel the contents of our stomach but also sometimes the proximal small intestine.