The reality of theosis (assuming you are one of the types of Christian who believe that theosis/ sanctification/ spiritual progression is the main purpose of human life - beyond salvation) - then this implies that what God wants for us is not just that we be happy (otherwise He would not want us to struggle - and theosis is a struggle).
God must want us to become like Him (or, at least, much more like Him than we spontaneously are).
That seems important and non-obvious.
God does not just want us to be happy. He does want that, but even more than He wants that, He wants us to mature: to grow-up.
Why? So we can be with Him. Thus, He wants us to grow-up and choose to love Him.
Why? - well, partly because He wants it. It is not just for our good; but for God's benefit too - the mutual benefit of Heavenly society, the Heavenly familty.