iTunes purchase low quality

I’ve recently purchased Apple TV 4K in the hopes of building a collection of movies and tv instead of buying blue rays.Some of the older content I’ve found doesn’t appear to be in hd never mind 4K.Looking at the preview for Jurassic park for instance, the quality of video and sound looks like my original VHS tape. This is a series of films I would really like to purchase on my Apple TV but I’m wondering if there is any point when the picture and sound are that poor even though it’s supposedly “4K”Is there a reason the content looks this way? Netflix and YouTube look fantastic and all the UI is very crisp but I’m just disappointed with the quality of some of the iTunes content.Is there anything I can do to fix this?Many thanks