This seems like a poor choice of technology rather than an outright nefarious decision. Polymer [0] uses the shadow dom api [1] extensively, but shadow dom v1 still isn't fully implemented across all vendors and shadow dom v0 is deprecated and slated for removal in April 2019 [2].
This feels more or less like some premature dogfooding of Polymer. It probably would've been advisable to serve the old version until modern non-Chrome browsers caught up, but Shadow DOM v1 will be implemented eventually so my guess is they made the decision to transition those users now.
How can you ever know someone's intent? I don't think it makes sense to assume malice in this case.
- Because YT makes money on eyeballs and runs on every terrible device specific browser under the sun. Making users experience worse intentionally only really hurts them.
- Because we're in a forum of devs that are all about chasing the latest features and polyfilling everywhere that doesn't have them -- it's practically SOP. I totally believe performance problems like this wouldn't get caught in testing when everyone has a corp network connection and powerful laptops/workstations.
I read a really good take once that I can't find anymore, but the gist was: sometimes a company knows about a poor decision or a bug, and just leaves it in because it gives them a competitive edge.
Deliberately and knowingly made decision that hurts already barely existing competition is not an innocent polyfill mistake. It's more like policy level abuse of dominant position to transition users to Chrome from non-Chrome browsers.
How would you tell the difference?