Let's think again that Bayern Munich, one of the big clubs that always dominates the Bundesliga, won't even let any club take the title from Bayern Munich's power and we'll see in the final match of the season whether there will be another surprise.
I wouldn't call them not letting anyone take the title from them, it is just an inconsistent performance from their competitors that allows them to win back points. Their closest rival Dortmund for example, always bottles their title charge near the season's end iirc. I don't know what factors affect their performance, but mentality must be one of them. I don't know what Leverkusen players' mentality is. Still, if they play without thinking about useless stuff they should be able to provide better challenges until the end of the season. At the very least, they are not Dortmund with their historic disappointing second-half results. CMIIW.