Main reason why Google decided not to support DNT is because user data is valuable to them. They don't want to respect your privacy because invading user privacy is their business model. Microsoft tracks people too via analytics and you can read about it on their site so you can't say it wouldn't cost Microsoft any money. Only advertising companies would say that DNT opt-in is intended.
>why doesn't Google respect the flag for those browsers now?
They need your data to personalize ads and make money out of it. It's Google's business model. It doesn't matter which browser you are using.
You can do something to make a real difference. First contact data controller ex. Facebook, Google or any company which doesn't respect your privacy and rights, tell them to stop. If they refuse to take action then contact your national data authority and they will investigate it for you. https://ec.europa.eu/info/law/law-topic/data-protection/refo....
I use and study math in hobby projects. I started enjoying math when I found out that I can do cool things with it. It's been long journey because I lacked motivation when I was a kid.