Simplify the following text for a Grade 7 native English-speaking person.
Original: It has also been said by many that Sianis put a `` curse '' on the Cubs , apparently preventing the team from playing in the World Series .
Simplified: Sianis became angry and cursed the Cubs , saying that they would never win a World Series as long as they played at Wrigley Field . Although the curse is often seen as a joke for most Cubs fans , some fans think it could be the reason why the Cubs have not won a World Series title .