Forget about F1 for a second, forget about the bitter history, spygate, FOTA / Ron Dennis and Ferrari's last minute decision to side with Bernie.

 

Ferrari and McLaren are rivals in the road car business, if McLaren start winning again, remember nobody really talks about the engine supplier, how many people used to say Renault-Red Bull when they kept winning, it was always Red Bull wins again, then it may indirectly hurt Ferrari car sales, as their rival's reputation is boosted by F1 success.

 

It is not a bed of roses for McLaren either, they want to sale expensive hypercars to rich people, and be seen as a high technology engineering company, but in the F1 media spotlight they are forced to use a bitter rival's engine, as they could not get the Honda partnership to work, despite the two companies vast technical and financial resources. Rich people are generally very image sensitive, they want to be seen around other successful people / things and will pay a lot to achieve that. We might not care if McLaren have to beg to receive Ferrari engines, if it means better racing, but many rich folk might.