Sure, I am not imposing a ultimate answer. It is just a discussion. But I do hope that you will consider what I posted. That there is another deeper layer (lack of a term) to consider the nature, essence and source of "God extending His love". It will transcend the thought of self-interest .... it is never even about us per se.
1 John 4:16 And we know and have believed the love which God has in us. God is love, and he who abides in love abides in God and God abides in him.
It is interesting that John does not say that God is love and that he who abides in God abides in love. Instead, he says that he who abides in love abides in God. To us, the former may seem more logical. But the latter is more practical and real. To say that we abide in God when we abide in love means that the very love in which we abide is God Himself. This indicates that the love that we have toward others should be God Himself. If we abide in the love which is God Himself, we then abide in God, and God abides in us. There is a union that we experience in His love.
There is no natural equivalent of this kind of description other than the love a man for a woman yet this is still too natural. I married my wife because of me i.e. I choose her out of attractiveness, personality, compatibility for my sake. And she also. Yet at times, there is glimpse that we do love for the others' sake.
The Bible do have a book, Song of Songs to describe this in type and picture:
Song of Songs is a romance between a great king (Solomon) and a country girl. However, these two do not match each other. In the same way, how could God with divinity marry a wife with humanity? They do not match. It must have been difficult for Solomon, the great king, to court a common country girl. If he had come to visit her in all his kingly glory, she would have been afraid of him. Therefore, the king became a "country man" in order to go to her village to court her, to gain her love. On the one hand, he made himself the same as the country girl; on the other hand, he made the country girl a queen. This is a type of the story of God's romance with man. He would marry a human being, just like the king would marry a country girl. Eventually, this country girl became Shulammite (a female version of Solomon), His counterpart.
Of course, we are not talking about teenage love

... got so much thrill LOL meh (hahahahahha). Well, there might be a little. But when we abide in God, there is freshness, sweetness and newness. When we say, "Lord, I love You" ... sure there is some. But that is just the consequence and result ... secondary.
Also, God wants to filled us with His love with which to love Him: The grace of the Lord which superabounded with faith and love in Christ to the apostle Paul for his dynamic and excellent salvation that he might be one of the greatest apostles ... 1 Tim. 1:14.
This layer of understanding, IMO, will put John 3:16 on another level. God loves <---- is not out of pitiful love but
a romance in a union of God man in the highest sense. It uplifts your statement, "God extended ..." thought the Bible uses "we loved because God loved us (1 John 4:19)
Then when we come to your verses in John 15:
15:9 As the Father has love Me, I also have loved you; abide in My love.
Out of abiding in His love (being filled), we go and bear fruit. The bearing fruit is the outflow of the divine love we enjoyed

Our work is the outflow of abiding in God (the earlier portion of John 15).
Paul said the same thing in Romans 5:5:
And hope does not put us to shame, because the love of God has been poured out in our hearts through the Holy Spirit, who has been given to us. Coupled with the verse above, he become the greatest apostle.
So, it is not from our perspective: "Oh I am weak, still selfish, but God still love me" .... Rather is, from God's view, "I will make you part of My Bride for My satisfaction because I love you". This is encouraging and full of hope

Jesus made it clear, they are two different commands. What you are saying about loving each other only fulfills the second command. It doesn't fulfill the first and the greatest command. Why I say that because of this verse,
It basically made a distinction between loving God and loving human, in which we must prioritize God over anything else. Abraham was told to sacrifice Isaac his son for God's sake. And he chose God over his son.
If we cannot reach the level of decision like Abraham, then our faith is not really faith. The truth is we don't have faith. Do you agree? Knowing this, does loving each other then suffice to meet God's standard of loving Him?
p.s. can we make it less tldr?