Blu Ray is not a Sony thing only. Panasonic, Pioneer, Phillips, and others were partners in developing it. Sony did not make DVD alone. Panasonic, Samsung, Toshiba. Phillips were all again partners. As a reminder, Panasonic also provided discs and drives to Nintendo systems. Sony has a history of its own proprietary storage that is more expensive or just not widely used. Beta Tapes. MiniDiscs. Memory Sticks and as for why Sony could screw over their own product? See UMDs and Vita Memory cards. The latter still costs several times more than a standard Micro SD card. $90 gets me a 400GB Micro SD Card. $80 bucks get me a 64GB Vita memory card. PS3 early on was very expensive partly because of the Blu Ray drive. At $600 it was the cheapest on the market. That is not cheap. PS2 with DVD cost $100 more than Dreamcast or Gamecube because of it.
The problem here, this proprietary SSDs is not a new tech nor different from every other SSD's except some few minor improvement and additional connector . When you see other patent from Sony , they have some modification to make it even more faster and have it's own CPU to have faster reading. Probably it will be slightly more expensives, but i bet it will not be like Vita was where every gamer need to have one as mandatory . This proprietary will help standardize the speed of SSD for PS5 because all games will be build based on SSD's ( unlike last gen where HDD is none factor). Game developer need to have one quality standard so every games will run the sames quality . Also Sony are likely to remove difficulty for PS gamer who are not found by opening PS to upgrade their Hard disc. Nvme or PC-i SSDs will be even harder to upgrade because they need direct connector to M.2 slot which is why they are making a solution for it.