You're quoting out of context. The first line of the email explicitly says he's taking time off to grieve, reflect and work on himself, in that order (he also enumerates "focus on building a leadership team" as a reason, though I'm not really sure how that is supposed to be done when one's taking time off)
The second paragraph (the one you quoted) is a tie-in to the third paragraph, where he says what's going to happen in terms of leadership during this interim period.
"If we are going to work on Uber 2.0, I also need to work on Travis 2.0 to become the leader that this company needs and that you deserve," Kalanick wrote in an email obtained by BuzzFeed News. "During the interim period, the leadership team, my directs, will be running the company."
It appears he is leaving more due to the issues with uber then him mom dying, but I am sure it contributed.