Playing by ear means you listen and are more likely to remember it. That is a fact.

With the greatest respect, it's not a fact - simply because some people do have great difficulty learning by ear, however much they listen and however much they try. They may not have been accustomed to listening for much of their life, or they may be some other reason. It's a skill that can be learned, but some people find it harder than others.

I've had pupils who could pick up a tune incredibly quickly - and others who couldn't hold a tune in a bucket.