The prosecutions are covered by the news. There is one in the UK today.

The point is that a foiled plot doesn't get reported on when it's discovered only when the offender goes to trial.

There is no public record of each arrest by the police, as an example which might help understand this.

Furthermore there will be plots that are foiled, people arrested but prosecutions dropped due to lack of evidence or something and, again, the press offices in the police or government are not mandated to distribute that news.