Safari doesn't have as many engineers (a shame) and definitely doesn't have as many people whose apparent job is just to sit on standards committees and generate specs (like Alex Russel, Justin Fangnani etc.).
They did end up proposing declarative template instantiation in 2017: https://github.com/WICG/webcomponents/blob/gh-pages/proposal... but that mostly went nowhere
It really is a shame Apple don’t invest more in WebKit and the web standards process. Although they’ve been doing a lot better over the past few years.