Because if you claim a player on waivers, his current team has three options: they can pull him back (in which case he can't be traded at all), or they can let you have him and his contract, or you can work out some kind of deal. If the player CLEARS waivers, then he can be traded for anyone not on the 40 before 9/1. So what probably happened in this case was that every team passed on him -- Cleveland didn't think they wanted to take on his salary right at that moment -- but then as time went on, they were like "yeah, let's do this."