(Not disagreeing at all, btw)
Many years ago a friend claimed to read a book a day. She was referring to cheap paperback fantasy books, her preferred genre. She could read them very fast because she already knew what was in them. She told me she mostly read the dialogue, which would definitely cut down on the time spent reading.
So perhaps the OP is reading mostly books they're already familiar with -- novels in a genre they like and nonfiction on topics they already mostly know. If so, you might be able to do similar things.
My father expected me to do so, at the age of 7, so I did. I don't think of it of speed reading - maybe it is. I did lose half my speed when I lived in Japan for a decade (learning to read in Japanese slowed my English input speed,