I have no scientific knowledge or background so the below is simply my assumption based on the reading I have done..... Therefore to be taken with a pinch of salt.
I'm guessing population density is one factor, for a highly transmissible disease, higher population densities will allow a decent spread of the virus.
Regional mobility (ie someone works 15 miles south of their home, their colleague lives 15 miles south of their work, that persons husband works 15 miles south of their home etc etc means that there is a lot of regional mobility to spread the virus).
Also, lack of sunlight and vitamin D deficiencies may be a contributing factor.
Ageing population meaning we have higher numbers of those in the more vulnerable categories.
Also as others have mentioned, our health care system means we may have higher rates of more vulnerable individuals, in countries with less developed health care systems perhaps they would not have survived to start with in order to be available to succumb to covid.
High levels of obesity.
The above is all pure opinion and none of it is fact...... It will be interesting to learn more about all this as time goes on.