You have a source for that? To me nobody really started caring about ServiceWorker until the big push recently for PWAs w/ launch of Lighthouse etc. Whereas devs have always wanted browsers to keep up with JS/ES/CSS language standards.
Also "development doesn't really work like that". Who's to say the same devs implementing ES6 features could take on ServiceWorker. Maybe there's something in the codebase blocking ServiceWorker. You just don't know. Assuming one thing is being neglected in favour of the other is a huge assumption.
I feel like the internet getting angry that 'feature 1' is released whilst the 'feature 2' they want isn't, and being all 'why are they spending all their time on feature 1 instead of working on my thing' is such an old trope there should be a term for it.
(But yeah I'd like to see ServiceWorker in Safari too, though please let's not bite the hand that feeds)!