The main motivator for doing so would be to sell it more cheaply to those who can’t afford the cocaine sold elsewhere as crack requires lower dosages for effect. You’ll find this in patterns of cocaine use already, the affluent use cocaine and the impoverished are more likely to use crack. I don’t think anything changes on that front with legalization except you trade arrests for outreach. I don’t see why we should expect demand for crack would suddenly grow and become more rampant with legalization, I’d expect the opposite, but in either case the solution is outreach not prohibition.