People are ridiculously scared of putting oil on their faces.
I think it's because people have been told since childhood that fatty oily foods cause break outs.
And people can't differentiate between the oils made by your skin and oils from other sources.
It's only necessary to cleanse once a day though. And the point of cleansing oils is that you combine make up removal and cleansing in one step. So a cleanser it is.
I think it's only necessary for people to cleanse once if their face is neither oily or very dry, but instead in between. I naturally have very oily skin (thanks to my lovely mother), and when I wake up in the morning and at night my skin is very "shiny" and I break out if I don't wash it. Literally, if I accidentally skip cleansing morning or night, my face is hell. Haha.