The premise in the title of your post is false.

Prepping can be - and must be - undertaken even during cataclysm, because every day you survive requires preparation for the next day.

The most important preparation to undertake is to gain knowledge and skills, because catastrophic events can cause physical changes in the environment that make physical objects instantly disappear. Knowledge and skills enable starting from scratch, which can be necessary without notice.

As you point out in the post itself, stores are potentially of great utility, so it isn't useless to have tools and necessities prepared in advance of their unavailability during disruption, but are not panacea that can solve every potential disruption. While it is necessary to learn skills and gain understanding at all times, it always has been, and it is never too late to acquire useful things.

I could not more vehemently disagree that it is too late, or that it ever could be too late, to do so, as long as our lungs breath air and our heart pumps blood in our veins. It is too late to prepare when the light goes out in our eyes, not our home. The minute your home has vanished in a flood, earthquake, or bombing, it is time to begin to acquire the necessities you lack, and since that can happen at any moment in time for myriad unpredictable and ineffable reasons, it can never be too late to prepare to live on as long as life remains to us.