The problem with DVD style covers for PS1 is that very few people are using that style. I considered it way back, but it would involve making covers for all games, including the ones that are already CIB and due to the number of PS1 games I have, it simply isn't feasible. Also, due to the square shape of the PS1 jewel cases, it's difficult to simply copy and paste the artwork onto a rectangular shaped DVD cover.
So the amount of work needed to create the covers is greater than most styles, and the number of people using that format is much less than most other styles. Therefore there isn't much supply to match the little demand.