Your example is a bad one. When you buy a new car you don´t hand the keys to others because the time others spend driving your car means it is unavailable for you. With digital media, sharing does not private you from accessing or enjoying the content. The distribution of said content generates a copy.
Sharing bought content has no direct repercussion in how you enjoy the media, it just has some risks in case of being identified by the seller.
This is a forum where we constantly watch content for free, and that content that is free for us has to be bought by others. Gatekeeping is, in essence, wanting all the rights to access to free content, without attending the moral obligation of giving back to others.
That being said, the psychology of individuals is complex, and there are certainly some valid motives that one can find to "gatekeep". Your example is probably not one of those, as it constitutes a logical error.