Do you mean you are just using water nowadays, or did you switch to using detergent or otherkind of cleaning formula?
I've been washing my hair with just water, and it works better than I expected. In the past, if I didn't wash my scalp before bed I'd feel itchy and sleep badly, but water seems to do a sufficient job of convincing my brain that I'm clean. When I feel sufficiently gross I use shampoo anyway. Conditioner is required to get a brush through it; my hair is very curly and will form knots if not brushed.
I am not planning on ceasing to use body soap.
You wash your hair and get rid of all the oil on the scalp protecting your skin. So your scalp makes as much as it can to replenish. Lather rinse repeat and now you've trained it to always go ham.
I've been washing my hair with just water for a year or so. I'm still oily, but much less so. When I have shorter hair it's on the high side of acceptable. When I have longer hair it's fine - just needs to get pulled down the hairs away from the scalp so it can do its full job.
Maybe you just got used to it? I shaved my head for a couple of years and it was still oily, just easier to clean. Shampoo, gel or soap don't seem to make a difference, and I'd rather not wash oily skin with just water.