I think, the instruction to eat sauerkraut within 2 days of opening is a precautionary measure to ensure food safety and maintain the quality of the product. While sauerkraut can still be safe to eat beyond the suggested time frame, its taste, texture and overall quality might deteriorate over time. It's also advisable to use clean utensils when scooping out the sauerkraut to prevent contamination.
The lactic acid produced by the bacteria also acts as a natural preservative, inhibiting the growth of harmful bacteria and extending the shelf life of sauerkraut.
And eating sauerkraut is a really good choice. Sauerkraut retains many of the nutrients found in cabbage, such as vitamin C, vitamin K and various B vitamins. The fermentation process can also increase the bioavailability of certain nutrients, making them easier for your body to absorb.
https://veganalyze.com/nutrition_facts_calories/sauerkraut_canned.html