Well, there probably is some reasonable upper limit that no human could reach without some sort of automated trolling. Just because 10 seems a bit small for some, does not mean that we could not have some other larger limit.
Further, I don’t think we should use concern about potential trolling as such a strong reason to dismiss the possibility of increasing the limit. This sort of rhetorical argument can be extended to all sorts of things…
Why allow people to play games at all? Or score their own games? Or send private messages? Or interact with other people at all? All of these are fertile ground for trolling.
In all of these sorts of interactions (from private messages to allowing people to open many game challenges), I think it is better to allow people the benefits having these features available, and then deal with the relatively rarer problematic behavior that might arise. If we place too much restrictions out of fear of trolling, then I feel like that’s an even worse impact of trolling. Imagine if we simply said “shut down the server, since trolls might come”.