Yeah its better, but it is still far from perfect. You aren't going to increase farm tractor or farm implement production by 50% with a year or twos notice. Some crops like fruits takes years to establish, and unused farmland quickly succumbs to nature and starts growing trees. And if that field wasn't clear 5 years ago you now have to stump grind or bulldoze the fields because tree stumps and tree roots will mess up your farm equipment, doubly worse if its some super massive tractor and implement setup that would normally be the most productive.

And there is also all the political and financial barriers to taking unfarmed land and very quickly turning it into farmland. Who owns it and who owned it before? Who with the right knowledge to manage it properly will run it? What about other problems around them that are part to the famine.

And farming in itself is not very predictable business. Yields regularly vary by 30% just due to local weather without being considered unusual. Return on investments may be a decade down the road even if everything is done perfect. Getting people to invest long term for a potentially very short term problem is not super easy.

We got surviving rations from back in the US civil war that are still edible, but people still regularly starved and had famines despite massive leaps in food preservation technology. Hermetically sealing just a single persons food for a year is not an easy task, not to mention hundred million+.

Economies of scale are huge here. You can store well below -40 when you're talking food for 100 million people, that just doesn’t work well when you’re talking one person.

Of note I didn’t say a year or 2’s notice 10 years of food on hand would be fairly cheap and we currently have the surplus to hit that number quickly. And that’s for 100% replacement, most situations aren’t going to drop food production to zero giving us more time.