Why the pages become images
A PDF page cannot be turned into editable PowerPoint shapes without guessing where every text box, image and alignment belongs. Converters that try produce decks of overlapping, misaligned boxes that take longer to fix than to rebuild.
A deck of accurate pictures is more useful than a deck of broken text. You can present it, annotate over it, add slides around it, and it looks exactly like the document you started with.
If you need the text as text, convert to Word instead and paste from there.