Yeah, the cells of most animals have the ability to make their own vitamin C, very likely including our ancestors if you go back far enough. The evolutionary reason why we stopped is probably simply because our bodies stopped needing to make it due to our fruit diet, so individuals that didn’t make the acid had a little bit more energy and nutrients to spare that would’ve otherwise been wasted to make it when it’s not needed. Over millions of years that small difference was enough for them to survive to parenthood slightly more often than their peers, slowly edging them out of the gene pool.

Evolution generally pushes bodies to conserve resources, so unnecessary things are usually dropped if the environment doesn’t require them for long enough. Kinda like how creatures living in dark caves eventually evolve to stop wasting the resources to make eyes and pigmented skin.