Bringing a really good player does have some risks involved. A player can get injured.
When any team is spending money for any player, they always have to remember the risk versus reward.
Bringing in someone like Kevin Durant is of course going to be a high risk, high reward move.
And that's exactly what's happening. He is getting injured but when he is playing he is actually playing well.
This kind of risk is given and it’s a small price to pay compared to the amount of contribution that a player can give both performance and popularity to the team which usually drives the profit of a team since many fans of that star player will now support his new found team.
The chance of a player being injured is very low also the management can check the injury records on a player before they will acquire him.