Diamonds not spawning.

I had recently created a survival Minecraft world in 1.16. After I had built my base I started on strip mining. I felt rather unlucky because after my first 3 iron pickaxes I had only found coal, iron, gold, and redstone. After about 3 hours of strip mining at y11 I decided to create a copy of the world in creative to see if there were any diamonds, there were but when I compared the 2 worlds there were only diamonds in the copy. (I do not remember what update I created the world but it was at least 1.16, and the copy was created in 1.16.3. I would like to add I might just be very unlucky.)