Since Real Madrid has won the La Liga title this season already and they have qualified for the UEFA Champions League finals, Ancelotti will not want to risk his best players getting injured. Ancelotti has been using Real Madrid players, who don't have playing time, to play some of their remaining matches, and they are pretty well performing. Villarreal only equalizes against Real Madrid because not all of their starting eleven played that match against Villarreal. Ancelotti wants his starting eleven to have a good rest so that they can perform well against Borussia Dortmund in the UEFA Champions League final.
The match was like a friendly to Real Madrid, they knew losing the game would not cause them any harm as they have already secure the La Liga title ahead of Barcelona that are many points behind them. We also have to appreciate Villarreal for taking the opportunity that was presented to them to draw the game because it would had been a disgrace that a B team of Real Madrid won them with the margins of goals. A. Sørloth was the star of the match by scoring four goals and giving Villarreal a point. The points was not very important to Villarreal as it did not help them to qualify for champions league football but they did not lose to a weak Real Madrid side and this is what is important for their confidence playing the final game of the season and also coming into next season.