system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do Canadian websites end in .ca and U.K. Websites end in .UK but United States websites don't end in .us?
gpt
Basically because the US created the internet and the US government controlled all the non-country specific Top Level Domans (TLDs) in the early days (.com, .net, .org, etc). Some of them are still controlled by the US only like .mil and .gov. 

Countries had more control over their specific TLDs like .ca and .uk, so were more easily able to give them to businesses in their country. However the US had more strict rules for getting .us in the beginning while .com and .org had fewer restrictions. So the US got used to not using .us even though it is available (and more open) today.