Bayern is a big favourite with odds of x1.33, while betting on Leipzig, you can pocket x7.50. I think bookies underestimate Leipzig team a bit. Leipzig are horribly inconsistent this season, especially when we consider all competitions (i.e. including the Champions League) but they still have one of the best defence in Bundesliga (second only to Bayern) and they noted a good performance last weekend when they earned 3 points on Eintracht (something that Bayern failed to do, as they drew with Frankfurt 3-3 back in October).
I actually do not think it is them underestimating the Leipzig team. Because they have been so inconsistent in this season it is highly unlikely that they are going to win the match against the team that is on the top of the table. They have lost the previous match against Mainz. But I do not think they are going to lose this one. I think they are at least going to get a draw and one point from this match. I know that the people have underestimated Leipzig but I don't think Bayern Munich is going to make that same mistake.
In essence, Leipzig is not a weak team but the bookie strongly favors Bayern Munich based on the available odds, because if the bookie does not underestimate Leipzig then of course the odds are not so wide like that. But yes, I also realize that the bookie has its own percentage to give their odds and therefore, some gambling sites have different odds but the point is that they are very favorable to Bayern Munich.
After all, Leipzig is also not a mediocre team and also not a completely weak team, with Leipzig's success in competing strongly in the top four at least it is proof that Leipzig has a quality that cannot be underestimated at all. So, although Bayern Munich are at the top of the standings and also play at home, basically it is also not a guarantee for Bayern Munich to be able to win easily, because of course Leipzig will make their best efforts not to lose even though Leipzig plays away.