I know that sounds too simple. But the Bible says we should fear Him because He is the Creator. Let the whole world fear the Lord, and let everyone stand in awe of him. For when he spoke, the world began! It appeared at his command (Psalm 33:8-9).
We should fear Him because He is holy. Who will not fear you, Lord, and glorify your name? For you alone are holy (Revelation 15:4).
We should fear Him because He is great among many other gods and idols He stands out. There is only One like Him. Great is the Lord! He is most worthy of praise! He is to be feared above all gods (Psalm 96:4).
And maybe most of all, we should fear Him because He is love! He loved us before we loved Him. He gave His Son to die for a sinful world. For as high as the heavens are above the earth, so great is his love for those who fear him (Psalm 103:11).
Fearing God means giving Him the awe and respect He deserves. We are called to fear God, not people!