What I don't get is the "why" for example Sony and Canon don't offer them with a PL-Mount.
As I'm sure you know, Sony and Canon do already make lenses with PL mounts. Sony has the Cinealta PL primes, and Canon makes a wide range of Compact and Studio PL zooms. As well, their CN-E primes can be converted to PL by Duclos Lenses.
If you're asking why these particular E mount zooms can't be converted to PL, it's all down to budget. Lens design is about making trade-offs. If you want longer flange depth, larger image circle, or brighter aperture, the lens elements need to be bigger which costs more.
Similarly, if you want more clearance between the rear element and the image plane, you need to add a retrofocal (reverse telephoto) lens group at the back of the lens. Which increases complexity and cost. This is why Angenieux's Optimo DP lenses can be made so much cheaper than their regular Optimo counterparts. It's basically the same lens, with the retrofocal elements removed. Of course, this means that the lenses cannot be used on mirror shutter film cameras or the Alexa Studio. But it was almost half the price when introduced, so people who only needed to use them on digital sensor cameras bought them.
The same difference applies here. The reason the E-mount zooms are so affordable is in large part because of the choice to design to a short flange depth. If you want to use them on PL mount, then you need to add complex rear optics. Which is exactly what Matt Duclos is working on right now. But it will probably be as expensive or more expensive than the lens itself. And it will make the lens slower and softer. Again, all because of the physics of light. It is what it is.