the usage of "such + singular countable noun"?

Such activity may or may not be illegal, and often involves cartels and lobbying for rules that benefit a firm at the expense of competitors and customers.

I read this sentence from an article. What really baffles me is that should it be "Such an activity" instead of "Such activity", since "activity" is a countalbe noun.

Solution 1:

More context:

But some billionaires are less upstanding, indulging in what economists call “rent-seeking”. This takes place when the owners of an input of production—labour, machines, intellectual property, capital—extract more profit than they would get in a competitive market. Such activity may or may not be illegal, and often involves cartels and lobbying for rules that benefit a firm at the expense of competitors and customers. Our analysis identifies industries where rent-seeking is common, including mining, defence, construction and casinos. This time it also includes the largest tech companies, since many of them have engaged in anticompetitive practices.

Activity doesn't have to be countable.

Examples from Longman Dictionary of Contemporary English:

Of course, all this illegal activity has its penalties.

Were the people you called engaged in illegal activities?

Take, for example, listening to music, which many people see as a leisure activity.

Other topics on which findings are ambiguous are the effects on leisure activity, crime, and degree of dependence on parents.