As a developer, it’s pretty difficult to integrate parallel code with a few particular events. Especially in RunService. Especially PreRender.
If you connect to PreRender, the render will be blocked until the connected thread is finished. This is an important feature of that event and few others like PreSimulation, PreAnimation, etc.
When you connect to PreRender you generally expect to do some work and then apply some change based on that work.
When you connect to PreRender in parallel you can do the work, but you must sync to apply the change.
But when you sync, you lose the render blocking feature since the desync thread ends.
So right now there’s really no way to connect in parallel and then do work and then apply it before the render happens.