Because the league hasn't signed off that they won't do anything to him. IMO, they will at some point come out and say they have investigated and unless other information comes to light they won't do anything to AB. How long do you think they won't do anything and THEN decide to punish him? That's pretty much doubling down on a punishment.
Look at Kareem Hunt as an example. There were similar incidents with ADP and Ray Rice. They missed almost entire seasons. Hunt was initially placed on the exempt list but then released right after. He sat as a free agent for awhile, then he was signed and suspended, and he ended up missing almost a year's worth of games. Essentially, they took what previously had been a year time out (whether it be by suspension, exception, or sitting as a free agent) to come up with a similar amount of time missed. They accomplished that by suspending him for 8 games when he could have been suspended a year. In Peterson's case, they actually tried to suspend him but that got appealed and eliminated. IIRC, all three of those cases involved the police and/or video or photographic evidence.
As of now and as far as we know , we don't have any of that with AB. Do people expect that he essentially misses the 2019 season and then he will still get exempted or suspended? Teams have avoided signing him because they would have to burn the money and cap room to not have him playing, which doesn't make a lot of sense.