Why can you only report someone for a maximum of 3 choices?

It probably has something to do with making sure that people put in the effort to tailor their reports to the most important offenses. Otherwise, players would simply check all the boxes out of spite, which would end up with even more useless data cluttering up some of the modules of the IFS. When it comes to the toxicity things, that's not really a problem. The system can scan for things rather efficiently, to the best of my knowledge.

But having a bunch of false reports submitted for intentional feeding, when the players aren't intentionally feeding, does have an effect. They are still working on getting FeederBuster fine tuned, and that requires accurate reports, not a bunch of junk from people who are pissed off at someone for losing lane. And it doesn't help that lots of the streamers have taken to using the phrase "inting" in a completely inaccurate manner. There's a huge difference in someone intentionally feeding and just making a dumb mistake. But when someone famous says it facetiously, it trickles down until you have all these fanboys and fangirls reporting people for "inting" because they tried something and failed.