This is the right answer. To complement it, I’d just say I’ve read someone before say that at Microsoft there’s no incentive to squeeze performance, so why bother if it won’t help you get promoted or get a bonus? All these things add up over time to make Windows only care about it when there is actually a huge bottleneck.
It’s also worth noting (for non programmers out there) that speed has no correlation with the amount of code. Often it’s actually the opposite: things start simple and begin to grow in complexity and amount of code exactly to squeeze more optimizations for specific use-cases.
They didn’t even bother to do a gradual rollout, like even small apps do.
The level of company-wide incompetence is astounding, but considering how organizations work and disregard technical people’s concerns, I’m never surprised when these things happen. It’s a social problem more than a technical one.