The question was more complex than the title given. The questioner asked why the Bible states that Adam sinned first, when in fact Satan sinned first. Furthermore, Adam and Eve were tempted by Satan, and therefore Satan clearly had sinned prior to meeting up with Eve and tempting her.
Satan attempted to usurp God because of his pride and was thrown out of heaven prior to verse 2 of Genesis chapter 1. He thus sinned and was the first created being to do so, but his sin was not unto death as in the case of Adam. Adam is flesh and blood, Satan is spirit. Adam's sin led to a physical death; Satan being spirit cannot die. For this reason Hell was made – where Satan and the one third of the angels who also sided with him will be thrown (Revelation 12:9, 20:7-10). Adam dies when he loses all his blood, for the Bible says that life is in the blood (Genesis 9:4) – Jesus Christ was dead and proven so, because he lost all his blood. Satan does not have blood and does not die.
Thus Satan was certainly the first to sin, but Adam was the first human to sin whose consequence is passed down to all other generations, in that all humans die. For this reason Satan is called a murderer – his tempting of Adam led to the physical death of all humans.
Note also the Bible does not say the Adam sinned first, but through Adam's sin death first entered the world (Romans 5:14). Paul points out to Timothy that in fact Eve was deceived before Adam sinned (1 Timothy 2:14).
Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned. Romans 5:12
We see here it was a man that introduced sin to the world – his name was Adam. If it had been Satan, an angel or some other spirit, the Bible would have said so.
The sin of Adam introduced death to the world and this death was passed down, through inheritance, to all descendants – we all die. Furthermore, the sin nature of Adam is also passed down through inheritance to all descendants and hence we are sinners at conception, requiring salvation.
For as in Adam all die, even so in Christ all shall be made alive.1 Corinthians 15:22
Satan, who is the devil, a created creature of the highest order (Ezekiel 28:14, 16), an anointed cherub (Ezekiel 28:14), sinned;
The devil has sinned from the beginning. 1 John 3:8
His pride led him and one third of the angels (who rank under him) to revolt in heaven (Ezekiel 28:17, 1 Tim 3:6), because Satan desires to be like God to the extent he would take on God with violence.
You were perfect in your ways from the day you were created, Till iniquity was found in you. "By the abundance of your trading You became filled with violence within, And you sinned; Therefore I cast you as a profane thing Out of the mountain of God; And I destroyed you, O covering cherub, From the midst of the fiery stones. "Your heart was lifted up because of your beauty; You corrupted your wisdom for the sake of your splendor; I cast you to the ground, I laid you before kings, That they might gaze at you. Ezekiel 28:15-17
Satan's sin was caused by unrighteousness – Ezekiel 28:15 which contrasts to the righteousness of God.
Your throne, O God, is forever and ever; a scepter of righteousness is the scepter of Your kingdom. Psalms 45:6
The earth was in existence at verse one of Genesis chapter 1 and it was at this time if not by this time that Satan had sinned.
In the beginning God created the heavens and the earth. The earth was without form, and void; and darkness was on the face of the deep. And the Spirit of God was hovering over the face of the waters. Genesis 1:1-2
Due to Satan's sin, he was cast out of the presence of God – where he was the guardian of the throne of God. He also lost control of the earth which at the time was covered in precious stones being first created this way.
You were in Eden, the garden of God; Every precious stone was your covering: The sardius, topaz, and diamond, Beryl, onyx, and jasper, Sapphire, turquoise, and emerald with gold. The workmanship of your timbrels and pipes Was prepared for you on the day you were created. Ezekiel 28:13
Some commentator's muddle the green leafy vegetable Garden of Eden found in Genesis with the Eden made of precious stones and other beautiful minerals where Satan first walked mentioned in Ezekiel 28:15. These are two different periods (and places) – many believe both are earth (as this author does); the precious stone garden came first where Satan walked, but when he sinned it was taken away from him, and the garden destroyed (or buried) after which God created the new garden in Genesis 1. We certainly know by verse 2 the earth was barren.
Adam's sin led to a physical death, a curse of all living creatures. For this reason Satan is called a murderer, for if Satan had not tempted Adam and Eve, they would not have sinned:
You are of your father the devil, and the desires of your father you want to do. He [Satan] was a murderer from the beginning, and does not stand in the truth, because there is no truth in him. When he speaks a lie, he speaks from his own resources, for he is a liar and the father of it. John 8:44