I meet all the requirements. I have all champs, a teammate or myself gets at least an S- on champs I have not received a chest for, and I never get chests. I have been 4 out of 4 available for a while. I play the game a lot and meet the requirements often, but never get a chest.
Your teammate has to be in your premade group to earn chests for you. You also can only get 1 chest per champion per season, so if you play the same group of champions you'll only earn a handful of chests. You can see which champions you've earned one for this season on your Champion page in your profile; if it earned one it will have a gold border and also show the chest when mousing over it.
You can read more about Hextech Crafting here; https://support.riotgames.com/hc/en-us/articles/207884233-Hextech-Crafting-Guide
Also note that you can lose Hextech loot eligibility by being punished, which you can read more about here; http://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/57wOcrmh-if-you-are-ineligible-for-hextech-loot-read-here-for-info-on-becoming-eligible-again
If you've read all that and are still sure you meet all the requirements, you can submit a Support Ticket.
Finally an answer as to why i have 50 key fragments and no chests. Just need to play more champs. THX!
