It's all about cumulative effect. He played a lot of tennis this year already and recently a bunch of clay tournaments and did decent at last couple MS events. I assume he's playing a grass event next week so it is a lot of tennis going into Wimbledon, even for a 20 year old.
It’s a fine line players in his position have to walk. They have to play enough to get their rankings up so that their draws become easier by avoiding the top players more, which allows a better opportunity to gain more points at the bigger events, all while risking injury by playing so much. Basically, they have to play more in order to play less.