It's called "crooking". Assuming this isn't just a variety that does this (many do), incomplete pollination, lack of water (overly dry soil, heat stress), and lack of good fertilization can do it. Also, cukes can get deformed if they snag on something while growing.

That being said, it's interesting that you can force them to grow straight. https://www.atlasobscura.com/articles/historic-gardening-tool