Moderator note: this post was originally in the light-weight same-type requirement syntax thread, but only because this thread was locked. We have re-opened this thread and moved this post to separate it from the technical discussion in that thread.
Someone asked for more information:
... but their post got deleted by a moderator; they asked me to follow up anyway. After consideration, I decided to respond, but the obvious thread is locked, so I'll respond here. If a moderator thinks this is off topic for this thread, please move it to that one or some other thread, or (if this is somehow considered off-topic for the Swift forums entirely) I can repost somewhere else on the internet.
In any case, Ted's simple answer in this thread is right, but there is of course more behind my decision to leave the Swift core team and the Swift Evolution community.
For context, I left Apple over five years ago and the only constant in my life is that I'm always "very busy" 
. That said, Swift is important to me, so I've been happy to spend a significant amount of time to help improve and steer it. This included the ~weekly core team meetings (initially in person, then over WebEx), but also many hours reading and responding to Swift Evolution, and personally driving/writing/iterating many Evolution Proposals. As such, my decision to leave the core team last summer wasn't easy.
To answer your question, the root cause of my decision to leave the core team is a toxic environment in the meetings themselves. The catalyst was a specific meeting last summer: after being insulted and yelled at over WebEx (not for the first time, and not just one core team member), I decided to take a break. I was able to get leadership to eventually discuss the situation with me last Fall, but after avoiding dealing with it, they made excuses, and made it clear they weren't planning to do anything about it. As such, I decided not to return. They reassure me they "want to make sure things are better for others in the future based on what we talked about" though.
On Swift Evolution, my original intention was to continue participating in the forums, but after several discussions generating more heat than light, when my formal proposal review comments and concerns were ignored by the unilateral accepts, and the general challenges with transparency working with core team, I decided that my effort was triggering the same friction with the same people, and thus I was just wasting my time. I don't think my feeling is unique here, e.g. this thread includes several community members who apparently feel they don't understand the real motivation for the proposal, aren't being listened to, and reached out to me because they thought I could help.
It is obvious that Swift has outgrown my influence, and some of the design premises I care about (e.g. "simple things that compose") don't seem in vogue any more. Equally obvious, I have many other interests than Swift, and no shortage of things to spend my time on. I am the sort of person who is always looking ahead, so while this situation is sad, I moved on and am definitely a lot happier not having to deal with it!
Swift has a ton of well meaning and super talented people involved in and driving it. They are trying to be doing the best they can with a complicated situation and many pressures (including lofty goals, fixed schedules, deep bug queues to clear, internal folks that want to review/design things before the public has access to them, and pressures outside their team) that induce odd interactions with the community. By the time things get out to us, the plans are already very far along and sometimes the individuals are attached to the designs they've put a lot of energy into. This leads to a challenging dynamic for everyone involved.
I think that Swift is a phenomenal language and has a long and successful future ahead, but it certainly isn't a community designed language, and this isn't ambiguous. The new ideas on how to improve things sounds promising - I hope they address the fundamental incentive system challenges that the engineers/leaders face that cause the symptoms we see. I think that a healthy and inclusive community will continue to benefit the design and evolution of Swift.
-Chris