* We like templates, and were able to implement a more efficient algorithm using them (even more than the recent improvements in Babel).
* Compatibility is important to us, so HTMLBars was going to be a much better transition story for Ember 1.x than JSX.
* We prefer an HTML-centric templating story (copy/paste valid HTML and it works) over an XML strategy that requires camelCasing, className/htmlFor, etc.
* We optimized Glimmer for a hybrid (rerender + subscriptions to the model or service layer) model that can opportunistically avoid work based on knowledge we have from the whole stack.
Fair enough, but I would argue JSX is just as "HTML-centric" as anything Ember has implemented, so long as we agree "HTML-centric" means, practically speaking, "not HTML."