Moses had spent 40 years in the desert. In contrast, the Israelites had spent generations living in the well-watered Nile delta, lacking for neither food nor water while being worked to death as slaves.
Now things were different. The workload was easier, but living in the desert was a harder life than living as slaves, and they made sure Moses knew about it:
16:3 ‘If only the Lord had killed us back in Egypt’, they moaned. ‘There we sat around pots filled with meat and ate all the bread we wanted. But now you have brought us into this wilderness to starve us all to death.’
So God supplied manna and quail and, when the Israelites ran out of water, God supplied that too.
Finally, God issued an ultimatum at Sinai:
19:4-6 ‘You have seen what I did to the Egyptians. You know how I carried you on eagles’ wings and brought you to myself. Now if you will obey me and keep my covenant, you will be my own special treasure from among all the peoples on earth; for all the earth belongs to me. And you will be my kingdom of priests, my holy nation.’ This is the message you must give to the people of Israel.
This was a good offer, and the Israelities agreed:
19:8 And all the people responded together, “We will do everything the Lord has commanded.”