The UK law is specifically designed to cover this. It's not some weird thing. Any "live TV" requires a license even if you watch it via streaming services.

If the law intends this, this is specifically a very weird thing. Why would the law intend to make people pay the BBC to watch UFC?

The law did not really intend this as it was written when "live TV" meant sitting in front of an actual TV. Since then it has been interpreted as covering everything, I think to protect revenues and deter even more people from ditching their TV licence.