Ameesha in particular was targeted because actresses like Kareena, who felt entitled to films as it was her family business, felt very jealous that an outsider scored two all time blockbusters in a row like Kaho Na Pyaar Hai and Gadar.
She made really nasty comments about Ameesha and how in KNPH every frame revolves around Hrithik to show him off. How Ameesha has no framers meant to showcase her and when she is visible, she has bad makeup or pimples showing. Very ugly comments about Ameesha's appearance.
Aishwarya got similar treatment because there was jealousy that around the same time Karisma broke out from Raja Hindustani and became a top heroine, Aishwarya made her debut and had major hits like Hum Dil De Chuke Sanam and Taal and thus took away from Karisma's spotlight. Kareena in particular was very angry that Aishwarya got the role in Devdas that Kareena had dressed up to audition for. A "nobody" getting all the big films was too much for her to bear and apparently Kareena used to make regular taunts about Aishwarya's fall from grace when she was fired from Chalte Chalte and was gleeful about it.
2