Because of their handmade nature - each piece will vary slightly in shape and size.
These lovely hand made pieces are special and if cared for properly can outlive us. I recommend you do not use a dishwasher to clean your ceramics. High temperatures, high pressure water and aggressive detergents can permanently damage glazes. Wash by hand with a mild soap and sponge.
Treat it with love and it will serve you for the rest of your life.