Your answer every time is "it's not half-man/half-monkey". It's the equivalent of me saying you don't have a picture of you as half-baby/half-adult, therefore you don't exist.
Evolution has been proven true to you many times. You either use the same old cop-out answers every time. Or completely ignore the evidence and dodge answering the evidence (e.g. vaccines created from evolutionary theory. Vaccines wouldn't work if evolution were false). Evolution is a fact. Sorry.
I think you are asking the wrong question. Why, as if I were to ask why that mountain exists. We know why, tectonic plates, continental shift, etc. But not why, as in suggesting it has some purpose. To me, there is no "why". Show me a "why" anywhere and I'll listen. But I haven't seen one anywhere.
Deep down you know you're wrong. The evidence against, the absolute absence of evidence for, and the complete illogical thought of an all-knowing, all-seeing, all-powerful, perfect being that f*cked up and didn't get what he expected is enough for any logical being to see the truth.
But you are not allowed. You do not believe what you believe because of evidence. You HAVE to believe it. 1.) It makes you feel better about yourself because it makes you feel important to know you know the hidden truth and the rest of the world is blind and wrong. Whatever happened in your life to make you need this self-esteem boost is up to you to analyze and ask yourself why you need it. 2.) You will lose your family and all your friends and will be isolated if you accept the facts for what they are. That must be tough. That would be difficult for any person to abandon. This is why cults have so much power over individuals.
Unfortunately, you are so deep in the JW cult and so brainwashed, you may never know the truth until your deathbed. 20 years may pass without the end of the world and you'll still tell yourself that it's coming, regardless of the advancement in science and knowledge.
You will have wasted so many years of your life. And I will be there to remind you. Like I said, Einstein was right, you do live in a poor way.