I think that ties into the habit that some people who've only ridden bikes where you can see the front wheel have of watching the front wheel as part of the steering / balance / knowing where you're going feedback loop. Not being able to see the front wheel breaks that, and it takes a little time to adjust. Which is harder if you're trying to learn to ride a recumbent (rather than say a cargo bike or Brompton with front luggage, which steers in a more familiar manner) at the same time.