Nobody expected so many defenders to be injured, and Ancelotti certainly doesn't want to be in that situation. But strangely, when it happened, and he had the chance to fix things (when the January transfer window opens), he did not take advantage of the opportunity, and it was as if he underestimated the problems they were facing. So for that reason, Ancelotti is indeed to blame for their failure.
I think that's the reason why he stepped down, because he felt he had made a mistake that made Madrid fail to win a trophy.
Dude, Ancelotti did his best. He isn't to blame for last season's defensive struggles.
He works his best with the squad he's given. Yes, management always accepted the advice and cooperation of the coach, so he has not built the Madrid squad alone.
55 defensive injuries over 3 season & more than 2000 days lost is not Ancelotti's fault. I have even seen midfielder Tchoumeni playing in defense in several matches.
Since their midfield and forwards are already elite, now they need to strengthen the defense. So this season, Real Madrid is going to add Trent Alexander-Arnold and Dean Huijsen to the squad. They will make the backline more stable, I think.
Ancelotti does not have full authority to recruit or release certain players in his squad, as it is known that the final decision regarding player transfers is in the hands of Florentino Perez, so I think Ancelotti cannot be blamed entirely. Many teams have the same fate as Real Madrid, where they ended the season without winning a trophy, the injury factor is the main reason that makes Ancelotti lack player options.
Next season with Xabi Alonso, Real Madrid will likely be able to perform much better, and perhaps the players who are currently undergoing treatment due to injury will recover in time. The recruitment of players like Trent Alexander Arnold and Dean Huijsen will certainly make Real Madrid defense line stronger.