Apple has stated reasons besides “control everything”. Many people dislike/disbelieve the reasons and have objections. It’s not worth litigating here (see: every thread anywhere mentioning iOS or Safari).
The point is, from a technical point of view there is only Safari on iOS. Chrome can’t add new APIs or rendering features that aren’t built into Safari.
And since Safari on iOS is very common and adds things when/if Apple decides, it’s often compared to IE6, rightly or wrongly.
(Not trying to debate the issues, just explaining the comment)