Because it's STUPID!
The sons of your father's sister are your first cousins.
Cousins of course!
benedict arnold
Cousine
aunts, cousins, daughters, sons, and friend.
Your uncle's sons and daughters are your first cousins.
third cousin once removed
basiclly there called brothers .-.-.-.-.-.-. basically* for one... and two no, they wouldn't be called brothers. If it was their parents sons then yeah, but if it's the sons of brothers then they'd be cousins. That's practically like saying one brother got married and had a son, then the other did too and had a son as well. The relation of the sons would be cousins.
Your son and your nephew are first cousins to each other. Their daughters are second cousins to each other.
Your granddaughter and your sister's grandson are second cousins.
Your uncle's wife is your aunt and her children are presumably his children, too. They are your first cousins. If your uncle's wife has children from a previous marriage, you are not related to them because you have no ancestors in common. However, if your uncle married her while the children were very young, they may effectively be treated as your first cousins.
Your first cousin is your son's first cousin once removed.