Why does apple only allow access from a Windows system if the user also owns a Mac device? No apple hardware results in no icloud.

Why does apple only allow access from a Windows system if the user also owns a Mac device? No apple hardware results in no icloud.

Somebody wanted to stream their photos to me and sent me an invite.

I setup an apple id and installed the icloud and eventually received

"Cannot Sign Up.

This Apple ID is valid but is not an iCloud account."

Google search indicated that you first need an apple hardware device to use the icloud and then it permitted Windows.