But, most clubs are just a business and they aim at either making as little loss as possible year to year and grow the clubs value more, or they want to even make a profit.
If Napoli wins the title this year, that means we are going to see them sell bunch of players, and make maybe 100+ million from sales, and sure still spend 40-50 million next year, but that means they covered more than a years costs, and the clubs value went up, so the owner could still sell it and make more money.
I forget the last time Napoli won the title. To be honest, since I started watching football regularly, I have never seen Napoli become champions of Serie A. They desperately need a title. They are well ahead of Milan and Juventus this season. They are in a safe place. Now if they are able to maintain consistency in their performance then they can win the title.
At the moment, there are no weaknesses in the Napoli team. But if they change the squad in the winter transfer, their performance is likely to be unstable. The Napoli coach will have to handle things very carefully.