Did God make offers He knew would not be accepted?
Yes. Scripture shows God made valid offers knowing they would not be accepted. Adam and Eve were offered continued garden life if they did not sin, but God knew they would. Israel at Kadesh Barnea was brought to the promised land's border, and Israel was also positioned to accept their King.
Les explains that God repeatedly made valid offers knowing they would not be accepted. In Acts 3:25-26, Peter tells the Jews they are the children of the prophets and of the covenant God made with Abraham, and that God sent Jesus to bless them by turning every one of them from their iniquities. Israel was then in a position to accept their King: the atoning work was done, Jesus had been raised from the dead, and He had ascended according to Psalms 110:1, ready to come back if Israel would just believe it. Les also points to Adam and Eve, who were made a valid offer to stay in the garden as long as they did not sin, though God knew they would, and to Israel at Kadesh Barnea, brought to the borders of the promised land with it all laid out before them.