The second reason is that the Lakers aren't fully healthy. It's a miracle that the Lakers even won 3 games without LeBron, thanks in large part to Carmelo Anthony's efforts.
The roster was constructed with LeBron James, Trevor Ariza, and Talen Horton-Tucker in mind as the wings of this team. Without them, Vogel has had to play the likes of Kent Bazemore a lot of minutes at the 3, which should be an indication as to why the defense hasn't been that good. With LeBron returning, look for the communication on both ends to improve the quality of play.
Much was made about the types of players the Lakers signed this off-season. All older veterans are well past their prime, but we've seen this time and time again. When you are a contending team, your roster heading into the playoffs will not be the same one you started with. The front office will do whatever to maximize the team's chance to make it to the finals, but a team in Los Angeles with LeBron will also naturally draw several buyout guys. It's hard to forecast who those guys are, but a guy like Terrence Ross will be a dramatic improvement over a guy like Kent Bazemore.
I still worry that some of the current veterans on this team aren't the type to play with maximum effort and commitment to the little things this early in the season. Westbrook deserves to be criticized for his sloppy play at the beginning of the season, but he isn't the only one. Players like DeAndre Jordan, Dwight Howard, and Rajon Rondo have not been playing their sharpest brand of basketball, but why should they? They all have been successful players in the past and can turn it on when they need to, right? I imagine with James back in the lineup and, the stakes become apparent, these veterans will start to clean up their act and buy into how Vogel wants them to play. If they don't, LeGM will waste no time getting rid of them like he did the 2018 Cleveland Cavaliers.