I think because the computer mouse is typically on the right side of the keyboard (because most people are right-handed), WASD has the advantage of allowing your mouse to be controlled by your right hand and you can keep your left hand in the normal position it is used for typing and not have to have your left hand move all the way to the arrow keys to control directions.

You awoke negative-nostalgia to membrane keyboards where I remember I couldn't hold Shift + W + A at the same time in Minecraft as a kid so you're definitely right about bad keyboards, but I remember dead keys on WASD as well. I wasn't there, but the largest consensus seems to be that Quake popularized it, plain and simple. I'm sure other factors like what you mention helped it become the dominant layout as well

edit: figured out why that nostalgia happened. I was revisiting an old flash game I liked [0] and people were complaining to the dev about this exact key ghosting issue to him when it wasn't his fault but a fault of their keyboards, and in the Newgrounds description he links to a forum post [1] elaborating on the issue

[0] https://www.newgrounds.com/portal/view/547881

[1] https://board.flashkit.com/board/showthread.php?789015-wont-...