If you need to invest a small/decent amount of money into stocks, Robos work wonderfully. It's a mass production angle -- good quality service at lower cost to many people; the Ford Model T of investing. Early robot just had a couple of investment options, and now there are more options but the same concept of limited choice at scale (Mustangs, Minvans, Trucks in my example)
Once you have estate planning and complicated tax issues, human advisors provide a lot of guidance to people that is hyper specific to you and your location / niche, which Robos just don't cover. Wealthfront, for example, won't arbitrate a dispute between beneficiaries of a family trust.
I think lawyers are a good comparison here. If you need some standard cookie-cutter incorporation docs, there's a bunch of websites where you can get some core documents for free or a few hundred dollars. But if you're afraid of making the wrong choice, or if you're in a situation that goes beyond the common scenarios (like M&A), then you hire a lawyer to provide you personalized advice.