Because even though they are currently 6 points behind Bayern Munich but with 8 matches left anything can happen, in football there are always unexpected surprises. Moreover, Bayern Munich has a concentration on the UCL league while Leverkusen does not. Of course this indirectly has a big impact on the Munich squad, especially if Kompany does not maintain the fitness of the players by rotating the players, the potential for losing points is very large.
The chances are indeed quite small even though Bayern Munich still have to focus on facing the Champions League and let's say Bayern Munich will lose in some of the remaining Bundesliga matches, but who can guarantee that Leverkusen will be able to win all the remaining matches. In football we know different things and unexpectedly Bayern Munich could lose in some matches, but is there a guarantee that Leverkusen can achieve a full victory.
Statistically Bayern Munich is much better and now they are six points ahead of Leverkusen so talking about chances I think Bayern Munich has much more potential to win the Bundesliga title this season.