In most of the US (it varies by state), moped riders (where mopeds are generally defined as motorcycles below a certain engine capacity and top speed, often 30 or 40 mph) do not need a license.

In the Netherlands, since about two decades, moped riders (<50 cc engine, <40 kph) need a license.

Quite possibly one of the reasons for this is that they share a lot of the infra with cyclists here.

I think having to ride a moped is a sufficient disincentive.

You're being silly, but this does impact the fastest growing segment of new bicycle riders: e-bikes. Right now, most states classify them as mopeds and may or may not require licensing accordingly, usually not. I don't know if there are any stats yet, since they are relatively new, but these e-bikes seem to me more dangerous in the hands of inexperienced riders than a traditional bike.

Indeed, pedestrians need no license.