private to public network

I have struggled with this repeatedly with Windows 7 and Windows 10. While there are solutions out there that describe how to change a network from Public back to Private (And not all solutions work because sometimes the options are not visible within Network and Sharing Center), I still cannot find out why this happens and it doesn't matter whether it is in a domain environment or workgroup environment. Is there a Windows Update that causes this?  I don't know, can anyone shed some light on this as to why this happens?  Why does a network, out of the blue for no apparent reason, switch from Private Network to Public network making the internet inaccessible?