Joseph's advice to Pharaoh for this warning was to appoint a foreman to prepare for the coming catastrophe.
41:33-36 “So now Pharaoh should look for a wise and discerning man and give him authority over all the land of Egypt. 34 Pharaoh should do this – he should appoint officials throughout the land to collect one-fifth of the produce of the land of Egypt during the seven years of abundance. 35 They should gather all the excess food during these good years that are coming. By Pharaoh’s authority they should store up grain so the cities will have food, and they should preserve it. 36 This food should be held in storage for the land in preparation for the seven years of famine that will occur throughout the land of Egypt. In this way the land will survive the famine.”
In the following verses, Joseph is named foreman and tasked with carrying out the preparation (vs. 41). He then does it in verse 48 and 49. However, you are right that there is only implication and inference of the Egyptians doing so on their own. That they went several years into the famine before approaching Joseph indicates some of them had been storing it up. I image that they thought Joseph's act of collection 20% of their harvests would carry them through the bad years. Perhaps they believed he would open the storehouses for free if the famine was as bad as Joseph said it would be. (I also imagine a significant number grumbling that this is just Pharaoh grabbing grain and not believing the warning.)
During the good years, the crops were excellent, and appear to have given more than double the harvest of a normal year. That would mean that even with Joseph's 20% tax, each farmer would have 160% of the grain from a normal year. If they sold all of their regular harvest, that still leaves 60% for them to do with as they please. Obviously, more than they would normally keep for next years seed and food for themselves.
In chapter 47, as the famine years have worn on, the people of Egypt are hungry and whatever they themselves stored has been used. We do need to remember that several years have passed at this point. There is no indication that the Egyptians went begging to Joseph before this point. Apparently, some of them had stored enough for themselves and for their neighbors.
Just thinking about human nature, some of them squandered their own excess during the good years in the belief the plenty would not end. All that remained was in Joseph's storehouses. Apparently, Joseph's 20% was enough to provide for all the people in Egypt and the surrounding nations for the length of the famine. However, they had to buy it with their money and then sell themselves into slavery.
In summary, that the individuals did not store (enough of) their own grain in preparation has a few possibilities. In all likelihood, the answer is a mixture of the below.
- Some did not believe the famine would come at all.
- Others did not believe the famine would be as severe as Joseph and Pharaoh claimed. Especially as time wore on in the good years, the threat of famine would fade away.
- They squandered their plenty in the good years thinking this was the new normal for Egypt.
- They thought what Joseph took with the 20% tax would be enough to cover them in the future and would be provided for free to them.
- They tried, but what they kept wasn't enough for the severity of the famine that came.