Deals are mutually beneficial. If Apple and Mozilla were both taking Google's offer it's because neither felt they had more to gain from developing their own search engine to compete outright in the meantime or from offering someone else's as a default. There might be something to the argument Mozilla isn't in a position to reject the money because they're sort of a shambling corpse at this point but Apple is about as far from a desperate company as you can get.
Yes but Google’s payments still make up around 25% of their net income which is pretty huge. Losing that would have a very significant effect on Apple’s margins and stock price
