"Sony’s software for processing ARW RAW files is called Imaging Edge. Like most first-party software from camera manufacturers, it’s terrible and unintuitive to use — and should be saved for situations like a high-resolution multishot mode where it’s the only method to use a camera’s proprietary feature."
I think the primarily reason is that they have great hardware developers and terrible software developers. So, having ARWs it is maximum they could provide to photographer, so they could take the files and run away from sony as soon as possible (i.e. do the rest in the better software).
Pentax could save DNGs, there are zero reasons for other companies not to do the same.