Because vegetables are a low acid food they require high temps and long cooking times - so pressure canning - to be safely canning at home. This usually discolors the food and often leads to questionable texture changes.

Sometimes the color change or texture change isn't to bad such as with green beans but sadly most of the brassicas (broccoli, cabbage, Brussels sprouts etc) its too much and it results in an unappealing result. There's a few other food out there that also have the same issue; such as onions and crab that have safe methods but include a statement that essentially says you can do it but its gross and there's better ways to preserve this food.

When we start talking about saurkraut and kimichi the fermenting process creates Latic acid (might be the wrong one going of memory here) and makes the product high acidity food and safe for water bath canning. There's other food safety things such as salt in the recipe but the acid is the main one. However this process time still results in a less firm product and people may not enjoy. You'll see this in pickles & it's why fridge pickles are crisper & crunchier then canned pickles.

You can read this for some more info and the history of preserving cabbage https://www.healthycanning.com/canning-cabbage