I'd also blame it on Mitchell Baker. She was a lawyer whose main contribution to Mozilla was writing it's license. After she was laid off from Netscape, she kept falling upwards in Mozilla until she was CEO. And even flush with dubious corporate money, she gutted engineering teams while more than 10x her salary until it reached 7 million.
The reason they take the money is because they need the money.
The reason they need the money is because they need so many employees.
The reason they need so many employees is because it takes so much work to implement a modern web browser.
The reason it takes so much work to implement a modern web browser is because the web has sprawling Living Standards. And users expect not just correctness but highly optimized jit.