That's not necessarily true. For example they might be doing polyfills that are slower than the native windows implementation.
I feel like I'm seeing a lot of this kind of thinking everywhere. The canonical example for me is lately is "he voted for Trump/Hillary therefore he must support groping/war/whatever".
I wish people would ease up on these kinds of deduction-based motivation attribution. It's my view that there enough self-professed unethical motivations for us to work against, without speculating. The speculation just muddies the waters.