When a team succeeds in winning any trophy which happens to be a major one, it's expected of the team to do their best in other to retain that trophy again. I'm football, it's believed that it's easier to win a trophy than to retain it because after winning a trophy, every other opponents you'll face in your quest to retain it will definitely know more about the tactics that helped you win which in response will do anything possible to stop you from conquering again.
Since the 2017/2018 season, there has not been a team that is as capable as Real Madrid. No team has been able to return to winning the UCL in a row. Only Bayern Munich and Ajax in the year have been going on for a long time. Bayern Munich winning in 1974, 1975, 1976 and Ajax winning in 1971, 1972, 1973.
Of course, with the arrival of stars like Mbappe and Endrick, I think Ancelotti is trying to defend the UCL Title. With a good financial condition, Madrid has a great opportunity to build a stronger team for next season.