Because facebook.

Also security issues, lack of privacy, lack of proper encryption, censorship, etc. among a long trail of reasons.

Also whatsapp founder quitting and leaving 850millions dollars on the table doing so over the way facebook makes money out of whatsapp and for th way facebook made him mislead the european commission to have them green light the sale of whatsapp to facebook. He also called repeatedly for people to get rid of Facebook services.

for exemple this: https://en.wikipedia.org/wiki/WhatsApp_snooping_scandal and this https://en.wikipedia.org/wiki/Reception_and_criticism_of_Wha...

whatsApp is end-to-end encrypted and has better encryption than most secure messaging (cough telegram). So stop spreading FUD.

It's also not related to the Facebook app so it makes no sense.