Trolling isn't a report option because it is vague as to the point of being meaningless, everyone has a different definition of what being a 'troll' entails which makes it useless as a means of defining behavior.
And even if everyone agreed that trolling meant something specific, for example a troll being someone who is doing something to intentionally antagonize their own teammates, even then it is to vague as it does not show how the person was being antagonistic. Were they talking to people in chat? Feeding kills? Purposely avoiding fights and never helping toward any victory conditions? And even then how well can you determine that what they are doing is their intentions as opposed to your interpretation of their intentions?
Trolling is such a catch all phrase that it simply is not helpful as a report option, if you want to report someone you should be able to define a specific behavior that person was doing that is the cause of your report. If you can't do this and have to fall back saying they were 'trolls' and that is why they should be punished then personally I wouldn't give your report any credence.
