The problem is that cobertura.excludeexcluding files / classes from your project from tools.
What you want to use is cobertura.ignore, for example,
cobertura.ignore 'java.util.logging.*'
which takes a regular expression of the class / method name to ignore.
Ant https://github.com/cobertura/cobertura/wiki/Ant-Task-Reference:
Cobertura , "" . perl 5 . , ignore. . , , excludeClasses.