Real Madrid have their most important match of the year coming up and so they have no motivation to play for a win over Betis today. Betis, on the other hand, have an opportunity to get into the Champions League zone. Therefore, I think Real Madrid will lose today, they are already La Liga champions anyway.
I think you are wrong, Real Betis have no hope of getting into the Champions League zone. Real Betis lost head to head against Sevilla, if Real Betis win against Madrid and Sevilla lost, Real Betis would still be under Sevilla. Real Betis will only finish in the Europa League next season