One troll ship of friends who got the multi-pack and are trolling together = 4 reports, the chances of bumping into more than one other person during the sales period are very high.
So within 3 matches you have the potential to use up more than 10 reports. How high do you want the limit to be?
Realistically in a random lobby you have 15 people that you could report, per lobby, there is no limit high enough so you have enough reports while being low enough to stop trolls and for Muse and Moderaters to handle.
If people weren't stupid enough to use the reporst system to be trolls, the limit wouldn't be needed, but guess what, people are stupid.
You could always just report the captain of that troll ship instead of the entire ship, if he is part of the trolling.