Couple main reasons: 1) BSD license vs a CopyLeft license. Edge, Opera etc don't want to push their changes back up. 2) Compatibility and performance is why Brave switched from Gecko to Chromium. 75% of the marketshare is chromium based browsers so sites will more than likely work with chromium browsers.
I don't why webkit is more popular. Maybe because it(Apple) is slow to adopt standards.
I don't why webkit is more popular. Maybe because it(Apple) is slow to adopt standards.