Is there any reason that you cant report someone...

Because if someone is hacking, the game will detect it most of the time, as it counts as a 3rd party program that interfers between the match starting and match ending.

You can report them via Riot's support though, which is the best thing to do.

Noobs would just abuse the "report for hackz0r" option in the post-game screen. Writing shit like "umg i lost he like totaly one-shot me umg must be hackidnsggsdgdhning fking l2p".

Because most people can't make the difference between a good player , and a cheater . And even less if the cheater is good at cheating.

If you think they're hacking, submit a ticket.

Provide as many details as you can.

I've been accused of hacking / using scripts in more pvp games than I can count. Have I ever hacked or used scripts? No. But that didn't change the fact that kids who get out played want an excuse for it. Unless it's an obvious exploit and you have video evidence, the likelyhood of any results - not likely.