The difference is that SK had a major outbreak a bit earlier, and yet their death rates are slowing... Just 3 recorded today. Or, to use new cases, the UK has +676 cases today (?, possibly yesterday), SK +93 (this even in the context of SK having a far more extensive testing regime). It's very clear if you find the graphs on
worldometers.
Take March 8th as an example; SK had more than 7,313 recorded cases, the UK 278. SK has increased by 1100, UK by more than 2000. Obviously those absolute figures don't look too different, but as percentages that's massive. And remember the UK is effectively only picking up serious cases (and maybe contacts with them?) at the moment, whereas SK has tested more than 270,000 people (UK 828 tests/million, SK 5,776 tests/million).