Please don’t take this the wrong way, but the answer seems obvious. Our bodies were not meant to zero carb. While many people can eat inferiorly for a long time without any seeming ill effects, the lucky ones get feedback more quickly (before long term deficiencies lead to disease).
More (or less) of a good thing is not always better. A low carb diet that lowers BG and insulin is good, but that doesn’t mean our bodies don’t need the nutrition that vegetables or fruit provides. Broccoli and kale are not ornamental plants.