The problem is that Cleveland is in "win now" mode. While Cleveland has the first overall draft pick, word is that Lebron would only return if there was two superstars waiting to play with him. Since Cleveland already has a superstar in the making with Kyrie Irving, it would need to trade for Kevin Love to get that second superstar. Love would potentially cost Cleveland at least the 1st overall draft pick along with 1-2 players (e.g. Dion Waiters, Anthony Bennett) and another pick in 2015. All that with no guarantee that Love will sign an extension.
Plus IF Cleveland gets Love for both 2014 picks and Anthony Bennett, and Love signs, there still is the possibility that Lebron will not like the supporting cast (resigning Spencer Hawes would be a must). Too many things would have to go perfectly. If it doesn't, Cleveland could potentially be set back another few years. For a young, starting out head coach, the situation would just not be a good idea.
However, if Cleveland were to be patient, Lue may work out. Cleveland still needs interior scoring (which Anthony Bennett was not able to resolve) and is really 2 players away from legitimately looking like a strong playoff team. The Luol Deng trade really didnt work out and word is that Dion Waiters is a cancer in the locker room. Tristen Thompson is good defensively but lacks a reliable offensive game. Zeller is pretty much a backup.