Comment by Aloisius

It would shield them from legal liability which is more than nothing.

That is the primary reason to ban UK visitors.

They do seem to be considering banning only users after the 7 millionth - 1 visitor every month to avoid being classified as category 1 instead. That would let them avoid some of the most onerous parts of the OSA that would require stripping anonymity from editors and censoring whatever Ofcom says is "misinformation" and "disinformation."