That's part of the frustration of how Canon operates. Instead of working from requirements inwards, they decide what tier they're targeting and select à la carte features which can be accommodated at that price point.
I mean did any 5D4 pros really state, when surveyed, that 8K video clips were a requirement for its successor?
Can you tell me any tech company that operates the way that you're saying? Apple or Samsung isn't going to drop the price in next year's model if features or components end up being cheaper than before. They might release a different product at a cheaper price point, but not change the price of their flagship phones. But Canon does the same. They have different price tiers of products.
And it's not like Canon is adding totally unrelated features to photography, like a bottle cap opener and tweezers. Sensors and processors are needed for both, they're very closely related. Like someone else mentioned, the 45 megapixels and 20 FPS we're getting is related to 8k. Eye-auto focus has got to at least partially be because of a video initiative if not primarily because of video that they could also implement for stills.
As for your last question, while I don't really do much video, I do remember how reviewers and pros are always complaining about the Canon's "cripple hammer" for not implementing enough features. And I remember how people complained about Canon not using the full sensor and instead forcing cropped 4K video. They didn't do that this time. So you could say that yes, pros were basically asking for it in its successor.
