Why we have to Fortnite with gold??

This thread has been made countless times on these forums. It's just how the Xbox ecosystem works. Free to play games have always required an Xbox Live gold account for any online multiplayer sections.

Sony also charges a subscription fee. They just have a few games that work differently.

And it also conveniently makes them more money of off an extremely popular game where Sony do not. You forgot to mention that vital and real part

Hi,

At this moment there aren't any plans to make free games playable without gold but maybe in the further gold isn't required to play free games online

Sony most definitely does have server costs, but the difference here is that Microsoft is better able to maintain the tens of thousands of servers across the world and the thousands of staff who are paid to maintain them to ensure as little downtime as possible.
Those people are then able to go home, feed their family and play the same games they help maintain. As a gamer who plays both networks, I can definitely feel the difference in up time and quality.

Take advantage of the free rewards systems and $1 gold sales Microsoft has in place. If done right, you can go a whole year without paying for gold and still have it.