[observationist]

It's simple - interfere with the competition, useless engineer job security, performative "working" , and bad incentives all around. They're on a gravy train and don't want the ad revenue to ever stop. A truly independent browser threatens that entire ecosystem, and that in turn results in collusion and patterns of behavior intended to make things nearly impossible to keep up with, even though the actually functional bits that consumers give a shit about haven't really changed all that much in the last decade. What Microsoft did with IE, all the major browser developers are doing now to reinforce their anti-competitive collective behavior and each can seek as much rent as possible from their respective walled gardens.