Because omniscience is based off omnipotence
Technically, omniscience and omnipotence are mutually distinct. Omniscience refers to the capacity to know everything. Omnipotence refers to having unlimited power. But neither is a requirement of the other.
God's omnipotence allows Him to choose to ignore you completely
That is probably the lamest super power I have ever heard of. I don't think kids will be clamoring to the comic book store to see the latest edition of the adventures of 'Ignore Man'.
Kidding aside, you don't need to be omnipotent to ignore anything. Us lowly humans do that all the time. Heck, my cat ignores me when she feels like it.
In this case, you will continue to exercise your freewill, God has no interests in knowing what you will do.
That goes counter to most religions I am aware of. But hey, if you subscribe to the Church of the Mighty Ignore, that is your prerogative.