This is a problem I have with the interpretation many have provided of the Christian God.
He creates many with heavy, cruel burdens that He could relieve in a heartbeat.
...
I agree with you that we should feel compassion for gays; it's a heavy burden.
OK, I'm not the best person to explain this, but I know your questions come from a very real place and are asked earnestly, so I'll try.
I guess the seemingly slightly flippant answer would be: "because that's the world we live in". That normal distribution curve requires the deviations on each end of the "normal" part of the curve.
Animals who do what they were born to do, tigers eating antelope, elephants pushing over trees to get at the leaves, sharks gnawing on the occasional surfer, etc., are doing exactly what they were designed to do and are not good or bad.
For reasons unknown to us, God decided to imbue us, animals at that point and made of the same "dirt" as were all other living things, with His spirit - his breath. This created in us a dual nature. We are children of God, but fully human/animal too. God directs us to transcend our animal nature and become more like Him, but our physical animal nature wars with that command.
God gave us instructions as to how to live our lives according to his instructions: Torah. We are supposed to do our best to live up to God's instructions, and we live in faith knowing that God will reward us.
Hopefully, others wiser than I can add to this.