Betis is rarely to lose, the match might end in draw since it hosted in Real Betis's home. The other teams can only score 1-2 goals to Real Betis, nothing more, so Betis has a strong defensive strategy.
I'm sure Madrid will win against Real Betis later, especially since Madrid's performance this season is much better than last season, in fact Madrid has only lost once so far.
We need to being objective to judge the performance of every team, not influenced by the popularity of the team. Actually Betis should able to beat Real Madrid, but they're just not lucky enough and only scored one goal from six big chances.
Both Madrid and Barcelona will always dominating La Liga, but it doesn't mean they will never lose or draw against other teams.