We don’t necessarily need them. It simply facilitates the practice for beginners who often have difficulties of eating anything raw, so they get more chances to find something they can eat raw to start with, and choose the food best suited to their current degraded health state. This can be specially helpful for sick people.
Of course, if there’s nothing edible raw currently available where you are, it can prevent starving! Otherwise, it’s perfectly possible to live with a “local” range of food, the condition being that this range is broad enough, taking into account the health state and particular needs of the person. As Alphagruis argue, it might even be better in the long run.
Third point, there’s a stronger temptation to eat cooked food when you have for example only walnuts, apples and a few species of fish to eat. It was found unsustainable to remain exclusively on raw paleo with such a limited food choice.
The situation seems to be somewhat different in US because grass fed beef and bison is constantly available in unlimited amount, but it’s not the case in Europe, Germany excepted, perhaps. If suitable meat is available during the hunting season only, then it’s a problem, particularly if appropriate eggs are also unavailable. I could only proceed with instinctive raw paleo nutrition because seafood, New Zealand lamb and Australian horse meat are imported in Switzerland. Plus, having only apples as a fruit in winter would have despised me.