It's just that now that there's a list of some things that are reviewable, things that aren't on the list won't count. The NFL went through a similar thing when they were getting challenges too. People would watch the film and correct really egregious stuff (like the official's calling the end of a game even though there was time left on the clock). Without people having to throw red flags or anything like that. Now that there's that system in place, they only fix things in the specific cir stances dictated by the rules. If you left the free-flowing reviews run along with challenges, you open yourself up to issues where the refs' judgment can play an even bigger factor. Like imagine some officials giving coaches "extra" reviews because they're more lenient or whatever. You wouldn't know what you need to burn your challenge on until you try it.
Really, the refs just missed the basket. It sucks, but had they ruled it missed and said that's not challengeable, they could have probably defended the ruling. Then the league could have made it challengeable with an emergency rule, and we could have moved on. Had they called it goaltending and just stuck with that, they could have let the normal challenge rules run as normal, everyone would be happy. Instead, they muddied it up at the time and may have made it worse after the fact. First year of this new concept though. They'll figure it out.