The article says it all. To please the fans. Some fans just have this weird mindset that idols are some kind of inhuman creatures who are born for them only, so they would never accept that their idols can have a life like any human being and go on dates. When they get a lover, those fans will think they betray them to be owned by someone else rather than enjoying life in a normal way.
And fans turning away means less money for the bosses. The bosses don’t care for anything, as long as they have money.
This is something weird I notice in Japanese idols and the K-Pop scene, although I don’t see the K-Pop bosses banning their singers from having affair. What are those fans thinking anyway?