Because there is no clear definition for the word bivouac. So for some people the meaning of bivouacking – for example, mountain camping with a one person tent – is already camping for others.
Nevertheless, it can be basically said that bivouacking is generally understood to mean an outdoor overnight stay with reduced means. Camping, on the other hand, places value on a certain level of comfort – the mere fact that you always have ” fabric over your head ” when camping and not when bivouacking in many cases speaks for itself.
In Summer, bivouacking often doesn’t even require a bivy bag. If the weather is stable and the conditions are dry, and efficient sleeping bag is sufficient.