there is no Bundesliga team that is on par with Bayern to compete with them for the title.
Schalke is 17th in the points table. I think this is why the Dortmund team neglected the Schalke team. Dortmund should have performed very cautiously and found out Schalke's weaknesses and devised a match strategy accordingly. Although Schalke is in the 17th position in the table, the team has been performing well in the last few matches. Schalke's team is unbeaten in the last 7 matches.
Although Dortmund's striker's performance was good, their defence was weak in this match. Schalke attacked very little. Even then they managed to score two goals. I'd say it's because of Dortmund's poor defence. A strong and stable defence is definitely needed if you want to fight for the title.