That is like always, on the one hand people (in this case many developers) want more control of that what happens, but on the other side, they don't want the responsibility to manage all themselves. IMHO this is why Vulkan & DX12 aren't used in more games. DX11 makes it quite easy to get and keep something running. On Playstation they don't have a choice, they must go through this. It is like always, if you have the choice between the easy way and the much more complicated way, you always choose the easy way, especially if all your refined tools use the easy way and you have knowledge how the easy way works. But it is also a cost decision as more time equals more costs so even if they want to implement a DX12 mode, they might be forced to just implement the old way.
E.g. I'm currently playing Elex 2. The developer of this game still uses their own engine they made for Gothic 3 (released in 2006). In interviews they always stated they still use their old engine, because they don't want to start from 0. Their small team knows their tools and engine quite well so they are still using it, even if it looks a bit outdated.