There was also a much wider array of browser engines at the time (MS had 2, Opera had 1, Firefox had much higher market share than it does today).
So KHTML/Webkit hardly had control over the web the way Chromium might because they never had the market share Chromium did, and further, they were never the dominant engine embedded in nearly every browser the way Chromium/Blink are now.
The usual answer I see is along the lines of "because Google is too big, has too much control". To reiterate the original argument in this thread: Chromium being open source makes this a hard sell.
Maybe there's another reason I've missed, though!
If I understand correctly, Edge, Opera, Brave, Vivaldi, etc are all running on the later type of Blink "fork".
Does Google still contribute to Webkit? I was under the impression that stopped a long time ago after Blink and Webkit sufficiently diverged.
I think the idea of gp's point about others forking code means the forkers can also influence the code because they control the fork.
Otherwise, if we take your comment at face value, we'd conclude that Google's contributions to Webkit means it can't "suddenly control the direction" of Apple's Webkit. That's true, but also becomes irrelevant because Google controls its fork of "Blink".
In other words, does Apple's Webkit control us that much? No, because it seems like Google's Blink/Chromium is sufficiently independent. If we go back farther in the timeline, are we concerned that KHTML controls us? No, because it seems like Apple's fork of Webkit is independent and not beholden to KHTML decisions.
If Microsoft really wanted to, it seems like they have the resources to do what Apple did to KHTML and what Chrome did to Webkit.