First, pre-cut isn't that much more expensive. Second, cutting is an accessibility thing now? A kitchen knife and 5 minute YouTube video should have anyone being to chop/dice without much trouble. And once they learn they will only get faster/better at it allowing them to use whole veggies adding more variety.
Yes, it's a boon esp. for old people who live alone, have mobility or sight issues, and don't trust themselves to hold a knife. It's also a convenience thing, but as you said, the general population can cut things just fine and won't suffer much without it; which isn't the case for this growing demographic.