Bike handling skills ARE important and rollers have a positive influence on how you ride. People who have lots of experience (especially BMX/MTB/CX ) already have skills that rollers won't really improve. But for many of us, riding rollers develops steering and balance skills that are a notch above what you learn just riding down the road. And they help you stay sharp.
That said, people don't ride rollers just to improve skills, they also train on them. In the era of the modern smart roller, the idea that you can do serious training indoors and either maintain or improve your handling skills at the same time is compelling. Rigid trainers are divorced from the actual physics of riding, which is going to be detrimental to your skills if you do it for long periods. For most triathletes, doing ZWIFT or Trainer Road sessions on a smart roller rather than a trainer will be an automatic skill booster and an easy way to get more benefit from the hours spent indoors.
That said, people don't ride rollers just to improve skills, they also train on them. In the era of the modern smart roller, the idea that you can do serious training indoors and either maintain or improve your handling skills at the same time is compelling. Rigid trainers are divorced from the actual physics of riding, which is going to be detrimental to your skills if you do it for long periods. For most triathletes, doing ZWIFT or Trainer Road sessions on a smart roller rather than a trainer will be an automatic skill booster and an easy way to get more benefit from the hours spent indoors.