Because
Exodus 15:23
And when they came to Marah, they could not drink of the waters of Marah, for they were bitter: therefore the name of it was called Marah.
Exodus 15:24
And the people murmured against Moses, saying, What shall we drink?
Exodus 16:2
And the whole congregation of the children of Israel murmured against Moses and Aaron in the wilderness:
Exodus 16:3
And the children of Israel said unto them, Would to God we had died by the hand of the LORD in the land of Egypt, when we sat by the flesh pots, and when we did eat bread to the full; for ye have brought us forth into this wilderness, to kill this whole assembly with hunger.
Exodus 17:2
Wherefore the people did chide with Moses, and said, Give us water that we may drink. And Moses said unto them, Why chide ye with me? wherefore do ye tempt the LORD?
Exodus 17:3
And the people thirsted there for water; and the people murmured against Moses, and said, Wherefore is this that thou hast brought us up out of Egypt, to kill us and our children and our cattle with thirst?
Numbers 11:1
And when the people complained, it displeased the LORD: and the LORD heard it; and his anger was kindled; and the fire of the LORD burnt among them, and consumed them that were in the uttermost parts of the camp.
Numbers 14:1-4
1
And all the congregation lifted up their voice, and cried; and the people wept that night.
2
And all the children of Israel murmured against Moses and against Aaron: and the whole congregation said unto them, Would God that we had died in the land of Egypt! or would God we had died in this wilderness!
3
And wherefore hath the LORD brought us unto this land, to fall by the sword, that our wives and our children should be a prey? were it not better for us to return into Egypt?
4
And they said one to another, Let us make a captain, and let us return into Egypt.
Numbers 16:41
But on the morrow all the congregation of the children of Israel murmured against Moses and against Aaron, saying, Ye have killed the people of the LORD.
Psalm 106:7
Our fathers understood not thy wonders in Egypt; they remembered not the multitude of thy mercies; but provoked him at the sea, even at the Red sea.
Psalm 106:8
Nevertheless he saved them for his name's sake, that he might make his mighty power to be known.
wherefore
Exodus 5:22
And Moses returned unto the LORD, and said, Lord, wherefore hast thou so evil entreated this people? why is it that thou hast sent me?
Genesis 43:6
And Israel said, Wherefore dealt ye so ill with me, as to tell the man whether ye had yet a brother?
Numbers 11:15
And if thou deal thus with me, kill me, I pray thee, out of hand, if I have found favour in thy sight; and let me not see my wretchedness.