Very simple thing: why seems "hacking" to be a not reportable reason? Damn it we all know Riots anti hacking systems and tools are, in comparison to other online games, pretty good. But we all also know that, although it is rare, there is the one or the other hacky player that somehow manages to bypass and use hacking tools, programms, exploits, or what might be more common favorable bugs.
Damn it yes, I just got one terrible game that got me to such thoughs. A Ezreal/Morgana duo bot that does not miss a single skillshot within 25 minutes and capable of landing some through tiny minion gaps that are not even a third as big as Morganas Q hitbox actualy is. Exploiting any second an enemy is not behind a minion to poke and harass, is in Gold elo somewhat of skill. Being able to aim between minions, is somewhat of skill, and somewhat of luck involved. However, not missing a single skillshot aslong as there is sight to an enemy, suddenly missing every single one as those enter fog of war, admitting to be a x-skillshot based champion beginner, and last but not least, the duo partner playing also a skillshot based champion and also not missing a single shot under the same circumstances, at 2am, is in my opinion a very big reason to check if those 2 might be up to something.
Why not implement such a report? It is not like people would report everyone as "hacker". People that frequently report select whatever they please to. Also there is a lot of players that exploit bugs in a few games and rankeds before bugged champions actualy are taken offline.. yet they are not punished for doing so.