The reason why you can't just use an SVG in PPT is that it's not editable. My workflow as an example (macOS):
I have graphics in PPT that I want to edit...I don't like PPTs tools so I used Designer instead. Copying from PPT to Designer works great - I get vectors and text that match what was on the PPT slide.
I edit the graphics and then want to put back in to PPT. Today with Designer (& Photo) every option for exporting that works with PPT simply ends up putting everything as a single merged image back on to the slide. Fine for me, personally - I can always edit in Designer and copy/paste...but there are hundreds of other people in my company and the vast majority use only PPT so would be better to paste in vectors & text elements, which any of my colleagues can edit directly in PPT.
SVG support was just added to PPT within the last week or two, so that tells you where MSFT is on solving this problem. Still, even the SVG format is a merged image. Better because it scales a little smoother, but still not editable as individual elements.
