Because their styles are too different and she should collab. with No Doubt.

I want collab with.. Jared leto, britney spears, katy perry, adam levine, nicki minaj and kesha tooo!

I love Lana, she is really incredible. I think a collaboration between the two of them would be an impact, and I hope to one day GaGa make a collaboration with her, would be really incredible. GaGa Del Rey ♥

because she doesnt want to...

She Has collaborated with Lana Del Rey. She said that one version of Princess Die is with her.

And Nicki Minaj and katy perry