Right now, if an Apple executive asks, "How does Apple make money working on Safari?" the answer is really clear: "Google pays us $18 billion annually."
After that money is cut off, an executive at Apple has to ask the question: "Why should we keep investing in Safari, instead of SwiftUI and Xcode?"
I'm sure we'd all love the answer to be, "We have plenty of money, so we should invest heavily in both," but that's not really how the world works, and certainly not how Apple works. Executives make hard choices about what to prioritize. This will be one of them.