A divider would make more problems. If it's high enough to qualify as a handrail, it's gonna clip handlebars and high-side the rider. Ouch.

If it's low enough to avoid handlebars, it's just an additional tripping hazard.

In other words, a no-win situation.

But an alternative would obviously be bright yellow paint and/or an LED strip. Bright lights would probably be the best solution for approaching the steps in the dark.

Too bad we live in such a litigious society we cannot utilize simple solutions for rolling wheels. Europe has about a BILLION stair ramps for rolling bikes up and down at transit hubs and in their cities. Here, that would be quickly sued out of existence.